Photodissociation of CH2. IV. Predicted resonance Raman emission spectrum of photodissociating 3CH2.

Predicted resonance Raman emission spectra of photodissociating 3CH2 excited in its first absorption band are presented. In the three-dimensional wave packet calculations, we used ab initio potential energy surfaces for both the 3B1 ground state and the first excited 3A1 state, and an ab initio transition dipole moment function. The resonance Raman emission of CH2 is similar to that of A state H2O in that it shows a strong progression in the symmetric stretch vibration. It differs from that of A state H2O in that it also shows a fairly strong progression in the bending mode, which results from the much larger anisotropy of the excited state potential of CH2 in the exit channel. Because the stretching vibrational wave functions of CH2 are much more normal modelike than those of H2O the ratio of the intensity of emission into the (vs=2, vb=0, va=0 state to the intensity of emission into the (vs=0, vb=0, va=2) state is larger for CH2 by more than an order of magnitude. The measurement of resonance Raman emission spectra of CH2 would yield the energies of the symmetric stretch fundamental and its overtones, which are unknown at present, and present the first empirical evidence concerning the first excited triplet state. [ABSTRACT FROM AUTHOR]