How Active Is the Bend Excitation of Methane in the Reaction with O(³P)?

Abstract

The role of bending excitation of methane in the reaction with O(3P) is investigated in a crossed-beam experiment. Previous theories predicted that either stretch or bend excitation of the reactant promotes chemical reactivity and that initial bending excitation of CH4 preferentially yields umbrella-excited CH3 products. Experimentally, both predictions for bend-excited reagent were not borne out in this investigation. We found instead that compared to the ground-state reagent, bend-excited methane yields more vibrational excitation of the hydroxyl coproduct. The first reported product angular distributions show predominant backward scatterings for both ground-state and bend-excited methanes, which corroborate well with a direct rebound reaction mechanism.

Correlated Dynamics of the O(3P) + CHD3(v=0) Reaction: A Joint Crossed-Beam and Quasiclassical Trajectory Study

“…[13][14][15]24,26 Only the relevant features are presented here. The O( 3 P)-atom beam was generated by photolyzing SO 2 (4−5% seeded in H 2 at total pressure of 12 atm) by an excimer laser at 193 nm near the throat of a PZT (piezoelectric translator) pulsed valve.…”

Communication: Imaging the effects of the antisymmetric-stretching excitation in the O(3P) + CH4(v3 = 1) reaction

“…[18][19][20][21][22][23] Zhang et al reported on the influences of the bending excitations of CD 4 and CHD 3 . 18 They found little rate-promotion and that when a bend-excited CD 4 /CHD 3 does react with O( 3 P), the initial bending energy, instead of flowing into the umbrella mode of methyl radical products as one might expect, is preferentially deposited into OD/OH vibrations. The former finding is now confirmed in a very recent theoretical study.…”

“…We note in passing that the discharge-generated O less intense than the previous photolysis one. 17,18 A trade-off was made in this study for the convenience of changing E c . Figure 1 depicts the relevant energetics of this study.…”

Communication: Experimental and theoretical investigations of the effects of the reactant bending excitations in the F+CHD3 reaction

“…[12][13][14][15][16][17] There have also been studies on bend-excitation in the O + CH 4 reaction. [18][19][20] However, apart from very recent computational studies on the F + CH 4 ͑v 4 =1͒ and F + CH 2 D 2 ͑v 9 =1͒ reactions, 21,22 the previous work usually focused on the late-barrier polyatomic reactions ͑the transition state has a product-like structure͒ and there is almost no prior study on bending-excited early-barrier reactions, such as the F + methane reaction. Indeed the Polanyi rules 23 predict that the translational energy is more efficient to activate early-barrier reactions than vibrational excitation ͑and the reverse is true for the late-barrier reactions͒.…”