Product State Resolved Study of the Cl + (CH3)3CD Reaction: Comparison of the Dynamics of Abstraction of Primary versus Tertiary Hydrogens

Abstract

The reaction of Cl atoms with the selectively deuterated isobutane, 2-methylpropane-2-d1, has been investigated under single-collision conditions using state-selective detection of the products by resonance-enhanced multiphoton ionization (REMPI) in a time-of-flight mass spectrometer. The reaction was initiated in a crossed, pulsed flow of the reagents by 355 nm photolysis of Cl2 precursor. The internal state distributions of HCl and DCl products, formed by abstraction of primary and tertiary hydrogen atoms, respectively, from the hydrocarbon reagent are reported. The degree of rotational excitation of both products was found to be very low. By comparison of the intensities of the HCl and DCl REMPI signals, the ratio of the yield of HCl to DCl product was found to be 3.3 ± 0.4. With the known speed and angular distribution of the Cl reagent, it was possible to obtain information on the product center-of-mass angular distributions from measurement of the masses 37 and 38 time of arrival profiles. The DCl product is found to be mainly backward scattered with respect to the incoming Cl atom, while the HCl product is sideways peaked. Inferences on the dynamics of the two possible abstraction pathways from these results are discussed.