Inelastic collision dynamics of vibrationally excited I2(X)

Abstract

Rotational and vibrational energy transfer rate constants have been measured for excited rovibrational levels of I2(X). Stimulated emission pumping was used to excite the levels v=23, J=57, and v=38, J=49 via the B–X transition. Laser induced fluorescence from the D–X system was used to follow the collision dynamics. Energy transfer processes induced by collisions with He,Ar,N2,O2,Cl2,I2, and H2O were investigated. Rotational energy transfer was found to be efficient for all collision partners. In accordance with classical models, the total rotational transfer rate constants were proportional to the collision momentum (except for H2O). The total transfer rate constants and the distributions of rotational levels populated by collisions were not dependent on the initial vibrational state. For colliders that are not good quenchers of I2(B), the rotational energy transfer dynamics of the X and B states were found to be very similar. For colliders that are good quenchers, comparisons of the X and B state dynamics show that quenching competes with rotational energy transfer in the B state. Vibrational energy transfer was characterized for all collision partners with the exception of I2, which appears to have a low vibrational transfer efficiency. Vibrational transfer was dominated by Δv=−1 steps. Multiquantum vibrational transfer was not observed. The dependence of the vibrational transfer rate constants on the initial vibrational state appeared to be weaker than the linear scaling predicted by the Landau–Teller model. Vibrational deactivation of I2(X) plays an important role in chemically driven oxygen–iodine lasers. Effective deactivation rate constants have been derived from the vibrational transfer rate constants. Estimates for the deactivation rate constants for O2 and H2O differ from those currently in use by almost an order of magnitude.