Mode- and Bond-Selective Reactions of Chlorine Atoms with Highly Vibrationally Excited H2O and HOD

Abstract

The measured OH product state distribution from the C1 + H20 (104)-) -HC1 + OH reaction reveals an energy disposal pattern that is similar to that in the analogous H i -H20 (104)-) -H2 + OH reaction. Of the 9700 cm-' available energy, approximately 6% appears in internal OH excitation, approximately 21% in product translation, and the remainder (about 73%) appears as internal HCl excitation. The result that most of the available energy appears as internal energy of the newly formed diatomic molecule supports a spectator picture in which the old bond does not participate in the reaction. We measure the bond-selective branching ratio for the C1 i-HOD ( 4~0~) reaction and find that initial excitation of the 0 -H bond favors the HCl + OD product channel by at least a factor of 40. Measurements of the relative reactivity of water molecules prepared in the 104)-, 104)+ and 103)-12) local mode vibrational states suggest that all three vibrational modes enhance the reactivity by approximately the same factor.

Vibrational State Control of Bimolecular Reactions: Discovering and Directing the Chemistry

“…Detection of the OH product of the reaction of water with Cl shows that it contains less than 6 kJ/mol (500 cm -1 ) of rotational energy and no vibrational excitation, [7][8][9][10] Measuring the Doppler width of LIF transitions used to detect the recoiling OH fragment shows that only about 20% of the available energy appears in translation and that roughly 75% of the available energy resides in the HCl product, most likely as vibrational excitation of the new HCl bond. 9 The reaction with H follows a similar pattern. 10 The appearance of most of the available energy for the reactions of Cl and H with H 2 O(|04〉 -) in the new bond suggests that the O-H stretch, the "old bond", is a spectator that does not participate in the disposal of the energy into the products.…”

The exothermic HCl + OH·(H2O) reaction: Removal of the HCl + OH barrier by a single water molecule

“…In the Earth's atmosphere, chlorine atoms produced by the ultraviolet photolysis of chlorine gas readily react with a wide array of hydrogen-containing compounds, forming the relatively stable HCl molecule. The Cl + H 2 O reaction has been the subject of the experimental 1-4 and theoretical [5][6][7][8][9][10][11][12][13] studies. Motivated by the desire to understand trends in energetics from the water monomer to water polymers, one purpose of this research is to address the reaction of the chlorine atom with the water dimer, Cl + (H 2 O) 2 → HCl + OH·(H 2 O).…”

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

“…In a series of experiments involving the reaction of H, Cl, and O atoms with HOD the groups of Crim [8][9][10][11][12][13] and Zare 14 -16 demonstrated that vibrational energy could be used to exert bond selectivity in reactions involving polyatomic reagents. In these experiments, vibrational excitation of the O-H stretch in HOD selectively enhanced the hydrogenabstraction channel, whereas the excitation of the O-D stretch led to the deuterium-abstraction channel.…”