THE BENDING DYNAMICS OF ACETYLENE

The dynamics and spectroscopy of (J=0) acetylene bending degrees of fr eedom are investigated using a reduced dimensional Hamiltonian. This H amiltonian is obtained by applying an adiabatic approximation to avera ge the vibrational Hamiltonian over the ground state in the three stre tch coordinates. Within this approximation, an effective bend force he ld is obtained by adjusting force constants in the adiabatic potential to improve agreement between experimental and theoretical eigenvalues . With minor modification, a global bend force field is determined tha t qualitatively describes the vinylidene vibrations and quantitatively describes the acetylene vibrations. This surface is compared to the r esults of a recent ab initio calculation. A dispersed fluorescence spe ctrum out of the excited (A) over tilde state, calculated from this mo del, is found to agree well with results of a recent experimental stud y. (C) 1996 American Institute of Physics.