ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
State-resolved experiments probing the dynamics in NO2#–NO2 collisions at high internal energies (17 500〈E〈18 000 cm−1) are reported. A sequential optical double resonance technique with sensitive laser-induced fluorescence detection has been employed for the assignment of states of NO2 in the energy range between 17 500 and 18 000 cm−1, a spectral region where the optically "bright" 2B2 state is strongly coupled to high lying ("dark") states of the 2A1 ground state and other electronic states. Subsequently, the decay of population and polarization following rotationally inelastic and elastic collisions has been probed directly using a time- and polarization-resolved optical double resonance technique. Total depopulation rates have been determined to be about 2–3 times above the Lennard-Jones estimate. The thermally averaged state-to-state cross sections have been derived from a master equation analysis of the kinetic traces. The rate constants have been scaled by angular momentum scaling expressions based upon the infinite order sudden approximation which were modified to account for dynamical restrictions on angular momentum and polarization transfer. Pure rotational energy transfer within a vibrational state turned out to be fast and dominating the collision dynamics, whereas rovibrational energy transfer was slower and proceeded with a lower efficiency. In addition, interesting propensity pattern for angular momentum and polarization transfer have been found. The individual state-to-state rate constants clearly indicated that rotational energy transfer in highly excited mixed (chaotic) states is still governed by pronounced propensities in J, K, and mJ changing collisions. Here mj is the projection of J on a space fixed axis, which is defined by the laser, and K is the projection of J on the body-fixed symmetry axis of the molecule. In particular, we have found a propensity for small changes of mJ in elastic and inelastic collisions, in accord with recently suggested theoretical models. Interestingly, we also found a considerably lower probability for ΔK changes in these collisions. The propensities found for ΔmJ and ΔK are discussed within the framework of dynamic (kinematic) collision models. The observed cross sections, their overall scaling behavior, as well as estimations of the Massey parameter are consistent with collisions following mostly a direct mechanism for rotational energy transfer rather than a complex forming mechanism. © 1999 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.478014
Permalink
