Hodge index theorem

The rigid rotor is a mechanical model that is used to explain rotating systems. An arbitrary rigid rotor is a 3-dimensional rigid object, such as a top. To orient such an object in space three angles known as Euler angles are required. A special rigid rotor is the linear rotor which requires only two angles to describe its orientation. An example of a linear rotor is a diatomic molecule. More general molecules like water (asymmetric rotor), ammonia (symmetric rotor), or methane (spherical rotor) are 3-dimensional, see classification of molecules.

Linear rotor

The linear rigid rotor model consists of two point masses located at fixed distances from their center of mass. The fixed distance between the two masses and the values of the masses are the only characteristics of the rigid model. However, for many actual diatomics this model is too restrictive since distances are usually not completely fixed. Corrections on the rigid model can be made to compensate for small variations in the distance. Even in such a case the rigid rotor model is a useful point of departure (zeroth-order model).

Classical linear rigid rotor

The classical linear rotor consists of two point masses $m_1$ and $m_2$ (with reduced mass $\mu =\frac{m_1{m}_2}{m_1+m_2}$) each at a distance $R$. The rotor is rigid if $R$ is independent of time. The kinematics of a linear rigid rotor is usually described by means of spherical polar coordinates, which form a coordinate system of R³. In the physics convention the coordinates are the co-latitude (zenith) angle $\theta$, the longitudinal (azimuth) angle $\phi$ and the distance $R$. The angles specify the orientation of the rotor in space. The kinetic energy $T$ of the linear rigid rotor is given by

$2T=\mu R^2[{\dot{\theta }}^2+(\dot{\phi }\sin \theta {)}^2]=\mu R^2(\dot{\theta }\dot{\phi })\left(\begin{array}{cc}1& 0\\ 0& {\sin }^2\theta \\ \end{array}\right)\left(\begin{array}{c}\dot{\theta }\\ \dot{\phi }\end{array}\right)=\mu (\dot{\theta }\dot{\phi })\left(\begin{array}{cc}{h}_{\theta }^2& 0\\ 0& h_{\phi }^2\\ \end{array}\right)\left(\begin{array}{c}\dot{\theta }\\ \dot{\phi }\end{array}\right),$

where $h_{\theta }=R$ and $h_{\phi }=R\sin \theta$ are scale (or Lamé) factors.

Scale factors are of importance for quantum mechanical applications since they enter the Laplacian expressed in curvilinear coordinates. In the case at hand (constant $R$)

${\mathrm{\nabla }}^2=\frac{1}{h_{\theta }{h}_{\phi }}[\frac{\partial }{\partial \theta }\frac{h_{\phi }}{h_{\theta }}\frac{\partial }{\partial \theta }+\frac{\partial }{\partial \phi }\frac{h_{\theta }}{h_{\phi }}\frac{\partial }{\partial \phi }]=\frac{1}{R^2}[\frac{1}{\sin \theta }\frac{\partial }{\partial \theta }\sin \theta \frac{\partial }{\partial \theta }+\frac{1}{{\sin }^2\theta }\frac{{\partial }^2}{\partial {\phi }^2}].$

The classical Hamiltonian function of the linear rigid rotor is

$H=\frac{1}{2\mu R^2}[p_{\theta }^2+\frac{p_{\phi }^2}{{\sin }^2\theta }].$

Quantum mechanical linear rigid rotor

The linear rigid rotor model can be used in quantum mechanics to predict the rotational energy of a diatomic molecule. The rotational energy depends on the moment of inertia for the system, $I$. In the center of mass reference frame, the moment of inertia is equal to:

$I=\mu R^2$

where $\mu$ is the reduced mass of the molecule and $R$ is the distance between the two atoms.

According to quantum mechanics, the energy levels of a system can be determined by solving the Schrödinger equation:

$\hat{H}\mathrm{\Psi }=E\mathrm{\Psi }$

where $\mathrm{\Psi }$ is the wave function and $\hat{H}$ is the energy (Hamiltonian) operator. For the rigid rotor in a field-free space, the energy operator corresponds to the kinetic energy of the system:

$\hat{H}=-\frac{{\hslash }^2}{2\mu }{\mathrm{\nabla }}^2$

where $\hslash$ is reduced Planck constant and ${\mathrm{\nabla }}^2$ is the Laplacian. The Laplacian is given above in terms of spherical polar coordinates. The energy operator written in terms of these coordinates is:

$\hat{H}=-\frac{{\hslash }^2}{2I}[\frac{1}{\sin \theta }\frac{\partial }{\partial \theta }(\sin \theta \frac{\partial }{\partial \theta })+\frac{1}{{\sin }^2\theta }\frac{{\partial }^2}{\partial {\phi }^2}]$

This operator appears also in the Schrödinger equation of the hydrogen atom after the radial part is separated off. The eigenvalue equation becomes

$\hat{H}{Y}_{\ell }^m(\theta ,\phi )=\frac{{\hslash }^2}{2I}\ell (\ell +1)Y_{\ell }^m(\theta ,\phi ).$

The symbol $Y_{\ell }^m(\theta ,\phi )$ represents a set of functions known as the spherical harmonics. Note that the energy does not depend on $m$. The energy

$E_{\ell }=\frac{{\hslash }^2}{2I}\ell (\ell +1)$

is $2\ell +1$-fold degenerate: the functions with fixed $\ell$ and $m=-\ell ,-\ell +1,\dots ,\ell$ have the same energy.

Introducing the rotational constant B, we write,

$E_{\ell }=B\ell (\ell +1)\text{<mrow data-mjx-texclass="ORD">with</mrow>}B\equiv \frac{{\hslash }^2}{2I}.$

In the units of reciprocal length the rotational constant is,

$\overline{B}\equiv \frac{B}{hc}=\frac{h}{8{\pi }^{2}cI},$

with c the speed of light. If cgs units are used for h, c, and I, $\overline{B}$ is expressed in wave numbers, cm⁻¹, a unit that is often used for rotational-vibrational spectroscopy. The rotational constant $\overline{B}(R)$ depends on the distance $R$. Often one writes $B_e=\overline{B}(R_e)$ where $R_e$ is the equilibrium value of $R$ (the value for which the interaction energy of the atoms in the rotor has a minimum).

A typical rotational spectrum consists of a series of peaks that correspond to transitions between levels with different values of the angular momentum quantum number ($\ell$). Consequently, rotational peaks appear at energies corresponding to an integer multiple of $2\overline{B}$.

Selection rules

Rotational transitions of a molecule occur when the molecule absorbs a photon [a particle of a quantized electromagnetic (em) field]. Depending on the energy of the photon (i.e., the wavelength of the em field) this transition may be seen as a sideband of a vibrational and/or electronic transition. Pure rotational transitions, in which the vibronic (= vibrational plus electronic) wave function does not change, occur in the microwave region of the electromagnetic spectrum.

Typically, rotational transitions can only be observed when the angular momentum quantum number changes by 1 ($\mathrm{\Delta }l=\pm 1$). This selection rule arises from a first-order perturbation theory approximation of the time-dependent Schrödinger equation. According to this treatment, rotational transitions can only be observed when one or more components of the dipole operator have a non-vanishing transition moment. If z is the direction of the electric field component of the incoming electromagnetic wave, the transition moment is,

$⟨{\psi }_2\left|{\mu }_z\right|{\psi }_1⟩={\left({\mu }_z\right)}_{21}=\int {\psi }_2^{*}{\mu }_z{\psi }_1\mathrm{d}\tau .$

A transition occurs if this integral is non-zero. By separating the rotational part of the molecular wavefunction from the vibronic part, one can show that this means that the molecule must have a permanent dipole moment. After integration over the vibronic coordinates the following rotational part of the transition moment remains,

${\left({\mu }_z\right)}_{l,m;l^{\prime },m^{\prime }}=\mu \underset{0}{\overset{2\pi }{\int }}\mathrm{d}\varphi \underset{0}{\overset{\pi }{\int }}{Y}_{l^{\prime }}^{m^{\prime }}{(\theta ,\varphi )}^{*}\cos \theta Y_l^m(\theta ,\varphi )\mathrm{d}\cos \theta .$

Here $\mu \cos \theta$ is the z component of the permanent dipole moment. The moment $\mu$ is the vibronically averaged component of the dipole operator. Only the component of the permanent dipole along the axis of a heteronuclear molecule is non-vanishing. By the use of the orthogonality of the spherical harmonics $Y_l^m(\theta ,\varphi )$ it is possible to determine which values of $l$, $m$, $l^{\prime }$, and $m^{\prime }$ will result in nonzero values for the dipole transition moment integral. This constraint results in the observed selection rules for the rigid rotor:

$\mathrm{\Delta }m=0\text{and}\mathrm{\Delta }l=\pm 1$

Non-rigid linear rotor

The rigid rotor is commonly used to describe the rotational energy of diatomic molecules but it is not a completely accurate description of such molecules. This is because molecular bonds (and therefore the interatomic distance $R$) are not completely fixed; the bond between the atoms stretches out as the molecule rotates faster (higher values of the rotational quantum number $l$). This effect can be accounted for by introducing a correction factor known as the centrifugal distortion constant $\overline{D}$ (bars on top of various quantities indicate that these quantities are expressed in cm⁻¹):

${\overline{E}}_l=\frac{E_l}{hc}=\overline{B}l(l+1)-\overline{D}{l}^2{(l+1)}^2$

where

$\overline{D}=\frac{4{\overline{B}}^3}{{\overline{\mathit{\omega }}}^2}$

$\overline{\mathit{\omega }}$ is the fundamental vibrational frequency of the bond (in cm^-1). This frequency is related to the reduced mass and the force constant (bond strength) of the molecule according to

$\overline{\mathit{\omega }}=\frac{1}{2\pi c}\sqrt{\frac{k}{\mu }}$

The non-rigid rotor is an acceptably accurate model for diatomic molecules but is still somewhat imperfect. This is because, although the model does account for bond stretching due to rotation, it ignores any bond stretching due to vibrational energy in the bond (anharmonicity in the potential).

Arbitrarily shaped rigid rotor

An arbitrarily shaped rigid rotor is a rigid body of arbitrary shape with its center of mass fixed (or in uniform rectilinear motion) in field-free space R³, so that its energy consists only of rotational kinetic energy (and possibly constant translational energy that can be ignored). A rigid body can be (partially) characterized by the three eigenvalues of its moment of inertia tensor, which are real nonnegative values known as principal moments of inertia. In microwave spectroscopy—the spectroscopy based on rotational transitions—one usually classifies molecules (seen as rigid rotors) as follows:

• spherical rotors
• symmetric rotors
  • oblate symmetric rotors
  • prolate symmetric rotors
• asymmetric rotors

This classification depends on the relative magnitudes of the principal moments of inertia.

Coordinates of the rigid rotor

Different branches of physics and engineering use different coordinates for the description of the kinematics of a rigid rotor. In molecular physics Euler angles are used almost exclusively. In quantum mechanical applications it is advantageous to use Euler angles in a convention that is a simple extension of the physical convention of spherical polar coordinates.

The first step is the attachment of a right-handed orthonormal frame (3-dimensional system of orthogonal axes) to the rotor (a body-fixed frame) . This frame can be attached arbitrarily to the body, but often one uses the principal axes frame—the normalized eigenvectors of the inertia tensor, which always can be chosen orthonormal, since the tensor is Hermitian. When the rotor possesses a symmetry-axis, it usually coincides with one of the principal axes. It is convenient to choose as body-fixed z-axis the highest-order symmetry axis.

One starts by aligning the body-fixed frame with a space-fixed frame (laboratory axes), so that the body-fixed x, y, and z axes coincide with the space-fixed X, Y, and Z axis. Secondly, the body and its frame are rotated actively over a positive angle $\alpha$ around the z-axis (by the right-hand rule), which moves the $y$- to the $y^{\prime }$-axis. Thirdly, one rotates the body and its frame over a positive angle $\beta$ around the $y^{\prime }$-axis. The z-axis of the body-fixed frame has after these two rotations the longitudinal angle $\alpha$ (commonly designated by $\phi$) and the colatitude angle $\beta$ (commonly designated by $\theta$ ), both with respect to the space-fixed frame. If the rotor were cylindrical symmetric around its z-axis, like the linear rigid rotor, its orientation in space would be unambiguously specified at this point.

If the body lacks cylinder (axial) symmetry, a last rotation around its z-axis (which has polar coordinates $\beta$ and $\alpha$ ) is necessary to specify its orientation completely. Traditionally the last rotation angle is called $\gamma$.

The convention for Euler angles described here is known as the $z^{″}-y^{\prime }-z$ convention; it can be shown (in the same manner as in this article) that it is equivalent to the $z-y-z$ convention in which the order of rotations is reversed.

The total matrix of the three consecutive rotations is the product

$\mathbf{R}(\alpha ,\beta ,\gamma )=\left(\begin{array}{ccc}\cos \alpha & -\sin \alpha & 0\\ \sin \alpha & \cos \alpha & 0\\ 0& 0& 1\end{array}\right)\left(\begin{array}{ccc}\cos \beta & 0& \sin \beta \\ 0& 1& 0\\ -\sin \beta & 0& \cos \beta \\ \end{array}\right)\left(\begin{array}{ccc}\cos \gamma & -\sin \gamma & 0\\ \sin \gamma & \cos \gamma & 0\\ 0& 0& 1\end{array}\right)$

Let $\mathbf{r}(0)$ be the coordinate vector of an arbitrary point $\mathcal{𝒫}$ in the body with respect to the body-fixed frame. The elements of $\mathbf{r}(0)$ are the 'body-fixed coordinates' of $\mathcal{𝒫}$. Initially $\mathbf{r}(0)$ is also the space-fixed coordinate vector of $\mathcal{𝒫}$. Upon rotation of the body, the body-fixed coordinates of $\mathcal{𝒫}$ do not change, but the space-fixed coordinate vector of $\mathcal{𝒫}$ becomes,

$\mathbf{r}(\alpha ,\beta ,\gamma )=\mathbf{R}(\alpha ,\beta ,\gamma )\mathbf{r}(0).$

In particular, if $\mathcal{𝒫}$ is initially on the space-fixed Z-axis, it has the space-fixed coordinates

$\mathbf{R}(\alpha ,\beta ,\gamma )\left(\begin{array}{c}0\\ 0\\ r\\ \end{array}\right)=\left(\begin{array}{c}r\cos \alpha \sin \beta \\ r\sin \alpha \sin \beta \\ r\cos \beta \\ \end{array}\right),$

which shows the correspondence with the spherical polar coordinates (in the physical convention).

Knowledge of the Euler angles as function of time t and the initial coordinates $\mathbf{r}(0)$ determine the kinematics of the rigid rotor.

Classical kinetic energy

The following text forms a generalization of the well-known special case of the rotational energy of an object that rotates around one axis.

It will be assumed from here on that the body-fixed frame is a principal axes frame; it diagonalizes the instantaneous inertia tensor $\mathbf{I}(t)$ (expressed with respect to the space-fixed frame), i.e.,

$\mathbf{R}(\alpha ,\beta ,\gamma {)}^{-1}\mathbf{I}(t)\mathbf{R}(\alpha ,\beta ,\gamma )=\mathbf{I}(0)\text{with}\mathbf{I}(0)=\left(\begin{array}{ccc}{I}_1& 0& 0\\ 0& I_2& 0\\ 0& 0& I_3\\ \end{array}\right),$

where the Euler angles are time-dependent and in fact determine the time dependence of $\mathbf{I}(t)$ by the inverse of this equation. This notation implies that at $t=0$ the Euler angles are zero, so that at $t=0$ the body-fixed frame coincides with the space-fixed frame.

The classical kinetic energy T of the rigid rotor can be expressed in different ways:

• as a function of angular velocity
• in Lagrangian form
• as a function of angular momentum
• in Hamiltonian form.

Since each of these forms has its use and can be found in textbooks we will present all of them.

Angular velocity form

As a function of angular velocity T reads,

$T=\frac{1}{2}[I_1{\omega }_x^2+I_2{\omega }_y^2+I_3{\omega }_z^2]$

with

$\left(\begin{array}{c}{\omega }_x\\ {\omega }_y\\ {\omega }_z\\ \end{array}\right)=\left(\begin{array}{ccc}-\sin \beta \cos \gamma & \sin \gamma & 0\\ \sin \beta \sin \gamma & \cos \gamma & 0\\ \cos \beta & 0& 1\\ \end{array}\right)\left(\begin{array}{c}\dot{\alpha }\\ \dot{\beta }\\ \dot{\gamma }\\ \end{array}\right).$

The vector $\mathit{\omega }=({\omega }_x,{\omega }_y,{\omega }_z)$ contains the components of the angular velocity of the rotor expressed with respect to the body-fixed frame. It can be shown that $\mathit{\omega }$ is not the time derivative of any vector, in contrast to the usual definition of velocity. The dots over the time-dependent Euler angles indicate time derivatives. The angular velocity satisfies equations of motion known as Euler's equations (with zero applied torque, since by assumption the rotor is in field-free space).

Lagrange form

Backsubstitution of the expression of $\mathit{\omega }$ into T gives the kinetic energy in Lagrange form (as a function of the time derivatives of the Euler angles). In matrix-vector notation,

$2T=\left(\begin{array}{ccc}\dot{\alpha }& \dot{\beta }& \dot{\gamma }\end{array}\right)\mathbf{g}\left(\begin{array}{c}\dot{\alpha }\\ \dot{\beta }\\ \dot{\gamma }\\ \end{array}\right),$

where $\mathbf{g}$ is the metric tensor expressed in Euler angles—a non-orthogonal system of curvilinear coordinates—

$\mathbf{g}=\left(\begin{array}{ccc}{I}_1{\sin }^2\beta {\cos }^2\gamma +I_2{\sin }^2\beta {\sin }^2\gamma +I_3{\cos }^2\beta & (I_2-I_1)\sin \beta \sin \gamma \cos \gamma & I_3\cos \beta \\ (I_2-I_1)\sin \beta \sin \gamma \cos \gamma & I_1{\sin }^2\gamma +I_2{\cos }^2\gamma & 0\\ I_3\cos \beta & 0& I_3\\ \end{array}\right).$

Angular momentum form

Often the kinetic energy is written as a function of the angular momentum $\overrightarrow{L}$ of the rigid rotor. This vector is a conserved (time-independent) quantity. With respect to the body-fixed frame it has the components $\mathbf{L}$, which can be shown to be related to the angular velocity,

$\mathbf{L}=\mathbf{I}(0)\mathit{\omega }\text{or}{L}_i=\frac{\partial T}{\partial {\omega }_i},i=x,y,z.$

Since the body-fixed frame moves (depends on time) these components are not time independent. If we were to represent $\overrightarrow{L}$ with respect to the stationary space-fixed frame, we would find time independent expressions for its components. The kinetic energy is given by

$T=\frac{1}{2}[\frac{L_x^2}{I_1}+\frac{L_y^2}{I_2}+\frac{L_z^2}{I_3}].$

Hamilton form

The Hamilton form of the kinetic energy is written in terms of generalized momenta

$\left(\begin{array}{c}{p}_{\alpha }\\ p_{\beta }\\ p_{\gamma }\\ \end{array}\right)\stackrel{\mathrm{d}\mathrm{e}\mathrm{f}}{=}\left(\begin{array}{c}\partial T/\partial \dot{\alpha }\\ \partial T/\partial \dot{\beta }\\ \partial T/\partial \dot{\gamma }\\ \end{array}\right)=\mathbf{g}\left(\begin{array}{c}\dot{\alpha }\\ \dot{\beta }\\ \dot{\gamma }\\ \end{array}\right),$

where it is used that the $\mathbf{g}$ is symmetric. In Hamilton form the kinetic energy is,

$2T=\left(\begin{array}{ccc}{p}_{\alpha }& p_{\beta }& p_{\gamma }\end{array}\right){\mathbf{g}}^{-1}\left(\begin{array}{c}{p}_{\alpha }\\ p_{\beta }\\ p_{\gamma }\\ \end{array}\right),$

with the inverse metric tensor given by

${\sin }^2\beta {\mathbf{g}}^{-1}=$

$\left(\begin{array}{ccc}\frac{{\cos }^2\gamma }{I_1}+\frac{{\sin }^2\gamma }{I_2}& (\frac{1}{I_2}-\frac{1}{I_1})\sin \beta \sin \gamma \cos \gamma & -\frac{\cos \beta {\cos }^{}\gamma }{I_1}-\frac{\cos \beta {\sin }^{}\gamma }{I_2}\\ (\frac{1}{I_2}-\frac{1}{I_1})\sin \beta \sin \gamma \cos \gamma & \frac{{\sin }^2\beta {\sin }^2\gamma }{I_1}+\frac{{\sin }^2\beta {\cos }^2\gamma }{I_2}& (\frac{1}{I_1}-\frac{1}{I_2})\sin \beta \cos \beta \sin \gamma \cos \gamma \\ -\frac{\cos \beta {\cos }^{}\gamma }{I_1}-\frac{\cos \beta {\sin }^{}\gamma }{I_2}& (\frac{1}{I_1}-\frac{1}{I_2})\sin \beta \cos \beta \sin \gamma \cos \gamma & \frac{{\cos }^2\beta {\cos }^2\gamma }{I_1}+\frac{{\cos }^2\beta {\sin }^2\gamma }{I_2}+\frac{{\sin }^2\beta }{I_3}\\ \end{array}\right).$

This inverse tensor is needed to obtain the Laplace-Beltrami operator, which (multiplied by $-{\hslash }^2$) gives the quantum mechanical energy operator of the rigid rotor.

The classical Hamiltonian given above can be rewritten to the following expression, which is needed in the phase integral arising in the classical statistical mechanics of rigid rotors,

$\begin{array}{lcl}T& =& \frac{1}{2I_1{\sin }^2\beta }{((p_{\alpha }-p_{\gamma }\cos \beta )\cos \gamma -p_{\beta }\sin \beta \sin \gamma )}^2\\ & & +\frac{1}{2I_2{\sin }^2\beta }{((p_{\alpha }-p_{\gamma }\cos \beta )\sin \gamma +p_{\beta }\sin \beta \cos \gamma )}^2+\frac{p_{\gamma }^2}{2I_3}.\\ \end{array}$

Quantum mechanical rigid rotor

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In 12 months 2013, c ommercial retails, shoebox residences and mass market properties continued to be the celebrities of the property market. Models are snapped up in report time and at document breaking prices. Builders are having fun with overwhelming demand and patrons need more. We feel that these segments of the property market are booming is a repercussion of the property cooling measures no.6 and no. 7. With additional buyer's stamp responsibility imposed on residential properties, buyers change their focus to commercial and industrial properties. I imagine every property purchasers need their property funding to understand in value. As usual quantization is performed by the replacement of the generalized momenta by operators that give first derivatives with respect to its canonically conjugate variables (positions). Thus,

$p_{\alpha }⟶-i\hslash \frac{\partial }{\partial \alpha }$

and similarly for $p_{\beta }$ and $p_{\gamma }$. It is remarkable that this rule replaces the fairly complicated function $p_{\alpha }$ of all three Euler angles, time derivatives of Euler angles, and inertia moments (characterizing the rigid rotor) by a simple differential operator that does not depend on time or inertia moments and differentiates to one Euler angle only.

The quantization rule is sufficient to obtain the operators that correspond with the classical angular momenta. There are two kinds: space-fixed and body-fixed angular momentum operators. Both are vector operators, i.e., both have three components that transform as vector components among themselves upon rotation of the space-fixed and the body-fixed frame, respectively. The explicit form of the rigid rotor angular momentum operators is given here (but beware, they must be multiplied with $\hslash$). The body-fixed angular momentum operators are written as ${\widehat{\mathcal{𝒫}}}_i$. They satisfy anomalous commutation relations.

The quantization rule is not sufficient to obtain the kinetic energy operator from the classical Hamiltonian. Since classically $p_{\beta }$ commutes with $\cos \beta$ and $\sin \beta$ and the inverses of these functions, the position of these trigonometric functions in the classical Hamiltonian is arbitrary. After quantization the commutation does no longer hold and the order of operators and functions in the Hamiltonian (energy operator) becomes a point of concern. Podolsky proposed in 1928 that the Laplace-Beltrami operator (times $-\frac{1}{2}{\hslash }^2$) has the appropriate form for the quantum mechanical kinetic energy operator. This operator has the general form (summation convention: sum over repeated indices—in this case over the three Euler angles $q^1,q^2,q^3\equiv \alpha ,\beta ,\gamma$):

$\hat{H}=-\frac{{\hslash }^2}{2}\left|g{|}^{-1/2}\frac{\partial }{\partial q^i}\right|g{|}^{1/2}{g}^{ij}\frac{\partial }{\partial q^j},$

where $\left|g\right|$ is the determinant of the g-tensor:

$\left|g\right|=I_1{I}_2{I}_3{\sin }^2\beta \text{and}{g}^{ij}=({\mathbf{g}}^{-1}{)}_{ij}.$

Given the inverse of the metric tensor above, the explicit form of the kinetic energy operator in terms of Euler angles follows by simple substitution. (Note: The corresponding eigenvalue equation gives the Schrödinger equation for the rigid rotor in the form that it was solved for the first time by Kronig and Rabi (for the special case of the symmetric rotor). This is one of the few cases where the Schrödinger equation can be solved analytically. All these cases were solved within a year of the formulation of the Schrödinger equation.)

Nowadays it is common to proceed as follows. It can be shown that $\hat{H}$ can be expressed in body-fixed angular momentum operators (in this proof one must carefully commute differential operators with trigonometric functions). The result has the same appearance as the classical formula expressed in body-fixed coordinates,

$\hat{H}=\frac{1}{2}[\frac{{\mathcal{𝒫}}_x^2}{I_1}+\frac{{\mathcal{𝒫}}_y^2}{I_2}+\frac{{\mathcal{𝒫}}_z^2}{I_3}].$

The action of the ${\widehat{\mathcal{𝒫}}}_i$ on the Wigner D-matrix is simple. In particular

${\mathcal{𝒫}}^2{D}_{m^{\prime }m}^j(\alpha ,\beta ,\gamma {)}^{*}={\hslash }^{2}j(j+1)D_{m^{\prime }m}^j(\alpha ,\beta ,\gamma {)}^{*}\text{with}{\mathcal{𝒫}}^2={\mathcal{𝒫}}_x^2+{\mathcal{𝒫}}_y^2+{\mathcal{𝒫}}_z^2,$

so that the Schrödinger equation for the spherical rotor ($I=I_1=I_2=I_3$) is solved with the $(2j+1{)}^2$ degenerate energy equal to $\frac{{\hslash }^{2}j(j+1)}{2I}$.

The symmetric top (= symmetric rotor) is characterized by $I_1=I_2$. It is a prolate (cigar shaped) top if $I_3<I_1=I_2$. In the latter case we write the Hamiltonian as

$\hat{H}=\frac{1}{2}[\frac{{\mathcal{𝒫}}^2}{I_1}+{\mathcal{𝒫}}_z^2(\frac{1}{I_3}-\frac{1}{I_1}\left)\right],$

and use that

${\mathcal{𝒫}}_z^2{D}_{mk}^j(\alpha ,\beta ,\gamma {)}^{*}={\hslash }^2{k}^2{D}_{mk}^j(\alpha ,\beta ,\gamma {)}^{*}.$

Hence

$\hat{H}{D}_{mk}^j(\alpha ,\beta ,\gamma {)}^{*}=E_{jk}{D}_{mk}^j(\alpha ,\beta ,\gamma {)}^{*}\text{with}{E}_{jk}/{\hslash }^2=\frac{j(j+1)}{2I_1}+k^2(\frac{1}{2I_3}-\frac{1}{2I_1}).$

The eigenvalue $E_{j0}$ is $2j+1$-fold degenerate, for all eigenfunctions with $m=-j,-j+1,\dots ,j$ have the same eigenvalue. The energies with |k| > 0 are $2(2j+1)$-fold degenerate. This exact solution of the Schrödinger equation of the symmetric top was first found in 1927.

The asymmetric top problem ($I_1\ne I_2\ne I_3$) is not exactly soluble.

Direct experimental observation of molecular rotations

For long time, molecular rotations could not be directly observed experimentally. Only measurement techniques with atomic resolution made it possible to detect the rotation of a single molecule. At low temperatures, the rotations of molecules (or part thereof) can be frozen. This could be directly visualized by Scanning tunneling microscopy i.e., the stabilization could be explained at higher temperatures the rotational entropy.

See also

• Balancing machine
• Gyroscope
• Infrared spectroscopy
• Rigid body
• Rotational spectroscopy
• Spectroscopy
• Vibrational spectroscopy
• Quantum rotor model

References

43 year old Petroleum Engineer Harry from Deep River, usually spends time with hobbies and interests like renting movies, property developers in singapore new condominium and vehicle racing. Constantly enjoys going to destinations like Camino Real de Tierra Adentro.

General references

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  Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
  
  Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
  
  A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
  
  The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
  
  There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang (Especially Section 2: The Rotation of Polyatomic Molecules).
• One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting
  
  In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
  
  Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
  
  Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
  
  A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
  
  The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
  
  There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
  My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
  My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 (Chapters 4 and 5)
• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
  My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 (Chapter 6).
• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
  My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
  My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
• 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
  
  My blog: http://www.primaboinca.com/view_profile.php?userid=5889534