Journal of Physical Chemistry A, Vol.108, No.39, 8089-8095, 2004
Intramolecular dynamics in the photofragmentation of initially vibrationally excited CH2Cl2
The intramolecular dynamics of dichloromethane was studied by applying vibrationally mediated photodissociation and photoacoustic spectroscopy. The parent species were initially excited to the second, third, and fourth C-H stretch overtone regions and subsequently photodissociated by similar to235 nm photons that also tagged the ground, Cl(P-2(3/2)) [Cl], and spin-orbit-excited, Cl(P-2(1/2)) [Cl*], state photofragments via resonantly enhanced multiphoton ionization. The Cl and Cl* action spectra revealed enhancement of their yield as a result of rovibrational excitation with a Cl*/Cl ratio of about 1/2. The action and photoacoustic spectra manifested a multiple-peak structure, which in terms of normal- and local-mode models is shown to be related to overtones of C-H stretches or combination bands of C-H stretches and bends. The measured time-of-flight profiles together with the determined Cl*/Cl branching ratios suggest fast dissociation and involvement of upper states of A' and A" symmetry, mixing via curve crossing and releasing both Cl and Cl*. The determined Cl*/Cl ratios in photodissociation of vibrationally excited CH2Cl2 are higher than those obtained previously in 193 nm photodissociation of the vibrationless ground state, implying higher nonadiabaticity for the former.