Vibrational and rotational energy transfers involving the CH B 2∑- v=1 vibrational level in collisions with Ar, CO, and N2O

Abstract

With photolysis-probe technique, we have studied vibrational and rotational energy transfers of CH involving the B 2Σ- (v=1, 0≤N≤6, F) state by collisions with Ar, CO, and N2 O. For the vibrational energy transfer (VET) measurements, the time-resolved fluorescence of the B-X (0,0) band is monitored following the (1,0) band excitation. For the rotational energy transfer (RET) measurements, the laser-induced fluorescence of the initially populated state is dispersed using a step-scan Fourier transform spectrometer. The time-resolved spectra obtained in the nanosecond regime may yield the RET information under a single pressure of the collider. The rate constants of intramolecular energy transfers are evaluated with simulation of kinetic models. The VET lies in the range of 4× 10-12 to 4× 10-11 cm3 molecule-1 s-1, with efficiency following the order of Ar < N2 O, reflecting the average over Boltzmann rotational distribution. The RET rates are more rapid by one to two orders of magnitude, comparable to the gas kinetic, with the trend of Ar < N2 O. The transfer rates decrease with increasing N and ΔN, proceeding via the ΔN=-1 transitions slightly larger than ΔN=+1. With the fine-structure labels resolved up to N=6, the fine-structure-conserving collisions prevail increasingly with increasing N in ΔN ≠ 0. The rate constants for the F2 → F1 transitions are larger than the reverse F1 → F2 transitions in ΔN=0 for the Ar and CO collisions. The trend of fine-structure conservation is along the order of N2