Energy-dependent energy transfer: Deactivation of azulene (S, Evib) by 17 collider gases

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Abstract
Collisional deactivation of highly vibrationally excited azulene in the electronic ground state was investigated using infrared fluorescence detection. Azulene (S0, E) was prepared with E≂17 500 cm−1 and E≂30 600 cm−1 by laser excitation at 600 and 337 nm, respectively. Advantage was taken of the fast internal conversion rate to S0 azulene from S1(600 nm) and S2(337 nm) electronic states. The collider gases investigated are He, Ne, Ar, Kr, Xe, H2, D2, N2, CO, O2, CO2, H2O, NH3, CH4, SF6, n-C4H10, and unexcited azulene. The results are expressed in terms of 〈ΔE(E)〉, the average energy transferred per collision, which can depend on the vibrational excitation energy E of the azulene. Using previously obtained knowledge of the dependence of infrared fluorescence intensity on E [M. J. Rossi and J. R. Barker, Chem. Phys. Lett. 85, 21 (1982)], two methods were used to obtain 〈ΔE(E)〉 values from the fluorescence decay curves: (1) an approximate method that considered only the average energy, and (2) solution of the full collisional master equation. Both methods gave 〈ΔE(E)〉 values that depend strongly on E. The limited experimental information on the identity of the energy-transfer processes operative in the deactivation of azulene is discussed. Additional experimental results on vibration-to-vibration energy transfer from azulene to CO2 are presented, which indicate that the emission at 4.3 μm observed previously [J. R. Barker, M. J. Rossi, and J. R. Pladziewicz, Chem. Phys. Lett. 90, 99 (1982)] originates not only from CO2(001), but from other states with one quantum of excitation in ν3. The experimental results are discussed in terms of models for energy transfer, which have appeared in the literature. It is concluded that only a superficial understanding exists and theory has lagged far behind experiments on energy transfer.