Molecular rotations and local modes

摘要

Rotational energy level structures of stretching vibrational states have been investigated in the XH2, XH3, and XH4type symmetrical hydrides. Transformations from standard vibrationndash;rotation normal coordinate Hamiltonians are made to internal coordinate representations which explicitly give the terms responsible for rotational coupling between the different local mode states. It is shown that the local mode relations between the vibrationndash;rotation parameters as given by Lehmann lsqb;J. Chem. Phys.95, 2361 (1991)rsqb; and by Halonen and Robiette lsqb;J. Chem. Phys.84, 6861 (1986)rsqb; make these Hamiltonians diagonal in the local mode basis. The effective vibrationndash;rotation parameters of overtones are then proved to obey the local mode relations closer and closer as the vibrational excitation increases. A simple vibrational model accounts well for the vibrational dependencies of vibrationndash;rotation constants in the case of SiH4, GeH4, and SnH4. thinsp;