Study on local mode vibrations of molecular vibrational excitation states in CH4,SiH4 and GeH4 with quasiclassical trajectory method

By using the quasiclassical trajectory method,changes of normal and local mode vibrationalexcitation energies with time are investigated for XH4 （X=C,Si,Ge） molecules.The results demonstrate thatin a CH4 molecule the coupling between C—H stretching vibration and H—C—H bending vibration is relative-ly large so that the energy transfer is fast;while in SiH4 or GeH4 molecules this coupling is relativelysmall and thus an obvious energy relaxation is observed.This implies that there exists approximate local modevibrations for certain vibrational excitation states.