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As part of an investigation of intramolecular energy transfer in jet-cooled 1B2u benzene, an extensive study of one photon 1B2u↔1A1g spectroscopy has been carried out. Our data lead to an assignment for ν8 in the 1B2u state (1516 cm−1), to a number of new assignments involving activity in ν18 and ν4, and they show that many of the higher vibrational levels in the 1B2u manifold are mixed. The activities of components of combination levels with different vibrational angular momenta have been observed and used to resolve several controversies concerning assignments in the 1B2u↔1A1g spectrum of benzene.

The ion-pair states of molecular iodine provide a unique system for studying the efficiency, selectivity, and mechanisms of collision-induced non-adiabatic transitions. Non-adiabatic transitions between the first-tier ion-pair states in collisions with molecular partners and rare gases are analyzed and discussed. The qualitative features of the rate constants and product state distributions under single collision conditions are summarized and interpreted in terms of appropriate theoretical approaches. Two mechanisms for the non-adiabatic transitions are clearly identified. The first, operative for collisions involving molecular partners possessing permanent or transition electrostatic moments, is highly selective. It connects the initially prepared level in the E 0 þ g electronic state with the near-resonant vibronic level of the D 0 þ u state with a minimum change of the total angular momentum. In an extreme quasi-resonant case when the gap between initial and final rovibronic level is less than 1 cm À1 , this mechanism has a giant cross section, 40 times that of a gas kinetic collision. An electrostatic model, which includes the coupling of the giant E-D transition dipole moment with a moment of the colliding partner and the semiclassical Born approximation, provides a plausible interpretation of this mechanism. A second mechanism is shown to govern collisions with rare gas atoms. It results in population of several ion-pair states and broad distributions over rovibronic levels. This mechanism is successfully interpreted by quantum scattering calculations based on the diatomics-in-molecule diabatic potential energy surfaces and coupling matrix elements. The calculations provide good agreement with experimental measurements and reveal different mechanisms for the population of different electronic states. Unexplained features of the non-adiabatic dynamics and directions of future work are outlined.

A combined experimental-theoretical study of the vibrational predissociation and product rotational distributions for high vibrational levels of He 79 Br 2

Articles you may be interested inNon-adiabatic transitions from I2( E 0 g + and D 0 u + ) states induced by collisions with M = I2( X 0 g + ) and H2O J. Chem. Phys. 136, 234302 (2012); 10.1063/1.4725541Long-range collisional energy transfer between charge-transfer (ion-pair) states of I 2 , induced by H 2 O and I 2 ( X ) Electric-field-induced g/u mixing of the E0 g + ( 3 P 2 ) and D0 u + ( 3 P 2 ) ion-pair states of jet-cooled I 2 observed using optical triple resonanceThe collision-induced electronic energy transfer that occurs when I 2 in the E(0 g ϩ ) ion-pair electronic state collides with ground electronic state I 2 has been investigated. We prepare I 2 in single rotational levels in vϭ0 of the E state using two-color double resonance laser excitation. The resulting emission spectrum shows that the nearby (⌬T e ϭϪ385 cm Ϫ1 ) D(0 u ϩ ) electronic state is populated. The cross section for collision-induced E→D energy transfer is found to be 18Ϯ3 Å 2 . A range of D state vibrational levels are populated, consistent with a model in which overlap between the initial and final vibrational wave functions is important, but modulated by propensities for small vibrational energy gaps and those energy gaps that are closely matched to the vϭ0→vϭ1 energy separation in the I 2 (X) collision partner.