Collisional dynamics of the IF B 3Π(0+) state. III. Vibrational and rotational energy transfer

Abstract

Rate constants at T=300 K for collision induced vibrational and rotational energy transfer within the IF B 3Π(0+) state have been determined using both cw and pulsed laser induced fluorescence. State-to-state vibrational energy transfer rate coefficients have been measured for IF(B; v′) collisions with He, Ne, Ar, Kr, Xe, N2, O2, and F2. Vibrational energy transfer has also been studied as a function of the initially excited vibrational level. Steady-state fluorescence emission from v′=3 has been analyzed to yield total rotational removal rate coefficients with the noble gases and N2 as collision partners. Vibrational energy transfer is generally inefficient; the thermally averaged cross sections for single quantum transfer (Δv=−1) from v′=3, σ(3,2), decrease from 1.2% to 0.3% of the gas kinetic cross sections, σg, for the periodic series He to Xe. For diatomic collision partners, the respective values of σ(3,2)/σg for N2, O2, and F2 are 0.014, 0.033, and 0.020. The Δv=−1 cross sections for the noble gases monotonically decrease with μ1/3 while no clear dependence on the collision reduced mass is observed with N2, F2, and O2. The vibrational transfer cross sections for the noble gases, N2, and O2 scale linearly with vibrational quantum number. The results also reveal that ‖Δv‖=1 transfer is at least an order of magnitude more probable than that for ‖Δv‖=2. Rotational energy transfer is the most efficient kinetic process in IF(B). The estimated efficiencies for total rotational energy transfer from J′=22 in v′=3 with the rare gases and N2 are typically 20 to 200 times greater than those for vibrational transfer. The rate coefficients range from (9.7±1.8)×10−11 cm3 molecule−1 s−1 for He to (1.1±0.1)×10−10 cm3 molecule−1 s−1 for Xe. The rotational transfer rate coefficients show a smooth dependence on both the collision reduced mass and the polarizability of the collision partner. The qualitative results of these experiments are discussed in relation to traditional energy transfer models.