Theory of pure rotational Raman transitions in the vibronic ground state of a tetrahedral molecule
It is well known that the polarizability tensor of a rigid tetrahedral rotor is isotropic. Hence, pure rotational Raman transitions in the vibronic ground state of a tetrahedral molecule are forbidden. However, the distortion of the molecule by centrifugal forces produces an effective anisotropic polarizability tensor, which depends on the components of the total angular momentum, and results in a pure rotational Raman spectrum. The purpose of this communication is to give explicit expressions for the polarizability tensor operator and the scattering intensity of the pure rotational Raman transitions. The feasibility of observing such transitions and an estimate of the relative intensity are given for the case of methane. The results presented here have been derived partially by considering the matrix elements of the linear normal coordinate terms in the polarizability tensor, between perturbed wavefunctions that were obtained by mixing the ground state with the degenerate excited vibrational states. The existence of similar ''forbidden'' pure rotational transitions in the far infrared region were established recently both on theoretical and experimental grounds.
- Research Organization:
- Ames Lab., IA
- OSTI ID:
- 7219968
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 64:12; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
10 SYNTHETIC FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKANES
CENTRIFUGATION
CRYOGENIC FLUIDS
ELECTRICAL PROPERTIES
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
FLUIDS
HYDROCARBONS
MATHEMATICAL MODELS
MATRIX ELEMENTS
METHANE
MOLECULES
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
POLARIZABILITY
RAMAN EFFECT
ROTATIONAL STATES
SEPARATION PROCESSES