Energy-dependent dynamics of large-ΔE collisions:: Highly vibrationally excited azulene (E=20 390 and 38 580 cm-1) with CO2

We report the energy dependence of strong collisions of CO(2) with highly vibrationally excited azulene for two initial energies, E=20 390 and 38 580 cm(-1). These studies show that both the distribution of transferred energy and the energy transfer rates are sensitive to the azulene energy. Highly excited azulene was prepared in separate studies by absorption of pulsed excitation at lambda=532 or 266 nm, followed by rapid radiationless decay from S(1) or S(4) to vibrationally excited levels of the ground electronic state. The appearance of scattered CO(2) (00(0)0) molecules with E(rot)> 1000 cm(-1) was monitored by high-resolution transient IR absorption at lambda=4.3 mu m. The average rotational and translational energies of the scattered CO(2) molecules double when the azulene energy is increased by a factor of 2. The rate of energy transfer in strong collisions increases by nearly a factor of 4 when the azulene energy is doubled. The energy transfer probability distribution function for Delta E > 3000 cm(-1) at each initial energy is an exponential decay with curvature that correlates with the energy dependence of the state density, in excellent agreement with predictions from GRETCHEN, a model based on Fermi's golden rule to describe collisional quenching of highly excited molecules. (c) 2008 American Institute of Physics.