We are
currently
investigating
photolysis
of vibrationally excited methylamine, CH3NH2, coupled with H
photofragments detection, facilitated measurements of action spectra
and Doppler profiles, reflecting the yield of the ensuing fragments
versus the vibrational excitation and UV probe lasers, respectively.
The jet-cooled action spectra and the simultaneously measured room
temperature photoacoustic spectra of the first to third N-H stretching
overtones exhibit broad features, consisting of barely recognized
multiple bands. These spectra were simulated and analyzed in terms of
simplified joint local mode/normal mode (LM/NM) and NM models.
Diagonalization of the vibrational Hamiltonians revealed model
parameters, through least square fitting of the eigenvalues to the
retrieved band origins, predicting well band positions and allowing
band assignment. The derived Hamiltonians determine the initial
pathways for energy redistribution and the overall temporal behavior of
the N–H stretches as a result of Fermi couplings and interactions
with bath states. The results indicate non statistical energy flow in
the V = 2 manifold region, suggesting the importance of coupling on
specific low order resonances rather than on total density of bath
states. The measured Doppler profiles suggest low average translational
energies for the released H photofragments, where in the dissociation
of methylamine excited to the higher overtones the H atoms exhibit
lower energy content, implying a change in the mechanism for bond
cleavage. These results enable obtaining some insight on the
dissociation dynamics.