Low-Temperature Rate Constants and Product-Branching Ratios for the C( 1 D) + H 2 O Reaction

Kevin Hickson (1)

1 ISM - Institut des Sciences Moléculaires

The gas-phase reaction between atomic carbon in its first electronically excited 1 D state and water has been studied over the 50-296 K temperature range using a supersonic flow apparatus. C(1 D) atoms were produced by pulsed ultraviolet multiphoton dissociation of carbon tetrabromide; a process which also generates ground state atomic carbon C(3 P). The reaction was followed by detecting product H-atoms by pulsed vacuum ultraviolet laser induced fluorescence. Two types of experiment were performed. Firstly, temperature dependent rate constants were derived by recording H-atom formation curves at various gas-phase water concentrations at each temperature. Secondly, temperature dependent H-atom yields were extracted by comparing the H-atom fluorescence intensities generated by the target C(1 D) + H2O reaction with those of a reference reaction. The second-order rate constants are large and increase to low temperature, while the measured H-atom yields are close to the theoretical maximum value of 2 above 100 K. At 50 K, neither rate constants nor H-atom yields could be derived due to H-atom formation by quantum tunneling in the activated C(3 P) + H2O reaction. The present results are discussed in the context of earlier work on the C(1 D)/C(3 P) + H2O reactions.

Domaines: Chimie théorique et/ou physique

Kevin Hickson. Low-Temperature Rate Constants and Product-Branching Ratios for the C( 1 D) + H 2 O Reaction. Journal of Physical Chemistry A, 2019, 123 (25), pp.5206-5213. ⟨10.1021/acs.jpca.9b03037⟩. ⟨hal-02322215⟩