SINGLET METHYLENE KINETICS - DIRECT MEASUREMENTS OF REMOVAL RATES OF A1A1 AND B1B1 CH2 AND CD2

Journal article

Rate constants for collisional removal of ã1A1 and b̃1B1 CH2 and CD2 have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH2(ã1A1) removal by He, Ne, Ar, Kr, Xe, N2, H2, O2, CO and CH4, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10-12 cm3 molecule-1 s-1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD2(ã1A1) by the rare gases. The rate determining step in removal by the rare gases and N2 is thought to be singlet-triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH2(b̃1B1) and three Σ vibronic levels of CD2(b̃1B1) have been measured and found to lie in the range 2.5-6.0 μs, and collisional quenching rates for CH2(b̃1B1) are found to be of the order of the gas kinetic collisional frequency. © 1981.

Authors: Ashfold, M; Fullstone, M; Hancock, G; Ketley, G

• Publication status: Published
• Journal: CHEMICAL PHYSICS
• Volume: 55
• Issue: 2
• Pages: 245-257
• Publication date: 1981-01-01
• DOI: 10.1016/0301-0104(81)85026-4
• ISSN: 0301-0104
• Language: English