Rotationally resolved reactive scattering: Imaging detailed Cl+C2H6 reaction dynamics

Abstract

The hydrogen atom abstraction reaction of Cl (2P3/2) with ethane has been studied using the crossed molecular beam technique with dc slice imaging at collision energies from 3.2 to 10.4 kcal/mol. The products HCl (v,J) (v = 0, J = 0-5) were state-selectively detected using 2+1 resonance enhanced multiphoton ionization. The images were used to obtain the center-of-mass frame product angular distributions and translational energy release distributions. Two general features were found in all probed HCl quantum states at 6.7 kcal/mol collision energy, and these features have distinct translational energy release and angular distributions, as described for HCl (v = 0, J = 2) in a recent preliminary report [Li et al., J. Chem. Phys. 124, 011102 (2006)]. The results for HCl (v = 0, J = 2) at four collision energies were also compared to investigate the energy-dependent dynamics. We discuss the reaction in terms of a variety of models of polyatomic reaction dynamics. The dynamics of this well studied system are more complicated than can be accounted for by a single mechanism, and the results call for further theoretical and experimental investigations.

Crossed-Beams and Theoretical Studies of Hyperthermal Reactions of O(3P) with HCl

“…Examples are the roaming mechanism in the photodissociation of formaldehyde to form H 2 + CO 58 and acetaldehyde to form CH 4 + CO, 59 an indirect mechanism that violates the kinematic limit in H + HBr f H 2 + Br 60 and H + CD 4 f HD + CD 3 , 61 and the chattering hydrogen atom mechanism in Cl + C 2 H 6 f HCl + C 2 H 5 . 62 These mechanisms lead to greater internal excitation in the products. As discussed above, the dominant mechanism for O + HCl f ClO + H at high collision energies does not correspond to motion near the minimum energy path.…”

Velocity map imaging the dynamics of the reactions of Cl atoms with neopentane and tetramethylsilane

“…25 Velocity map images for HCl products. The first method uses a calibration reaction for which the DCS is known from CMB experiments, 26,27 and the second is to use the outcomes of a comprehensive Monte-Carlo (MC) simulation of the experiments that is similar in spirit to the approach used by Suits and coworkers for a related experimental design. 80 In both cases an angular correction function is generated, and the two are similar in form and magnitude.…”

“…Cl + C 2 H 6 → C 2 H 5 + HCl (4) have been well studied both experimentally 17,18,22,[25][26][27]45 and computationally, [57][58][59][60][61] and the reactions of Cl atoms with propane 1,62-64 and n-butane 21,25,62 have been similarly investigated. The energetics and kinetics of these reactions are very similar to those for reactions (2) and (3); the reactions are all rapid and direct, have either a low or no barrier to reaction and the exothermicities of the primary hydrogen abstraction reactions are typically about -3 kcal mol -1 .…”

“…The velocity information was initially derived from analysis of time-of-flight (TOF) profiles obtained in a TOF mass spectrometer, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] but velocity map imaging (VMI) 19,20 has since become the method of choice. [21][22][23][24][25][26][27][28][29][30][31][32] The experimental measurements and dynamical calculations for H-atom abstraction reactions involving simple alkanes illustrate a wealth of dynamical behaviour. For example, the shape of the transition state, with near linear Cl-H-C moiety, is reflected in the low rotational excitation of HCl products; scattering angles are largely determined by impact parameter and their distributions can vary with product rotational and vibrational quantum states; 1 and the reactions of Cl atoms with methane and partially deuterated isotopologues exhibit reagent vibrational mode specificity, [4][5][6][7][9][10][11][12]14,15,[33][34][35][36]…”

Quasi-classical trajectory study of the dynamics of the Cl + CH4→ HCl + CH3 reaction

“…The vibrational excitation of the chattering trajectories displays the same distribution as the nonchattering trajectories, showing no sign of the enhanced internal energies suggested previously. 58 Some degree of the excitation of the umbrella mode is expected from geometric arguments, because prompt abstraction of an H atom from methane would leave the CH3 group in the tetrahedral geometry displaced along the umbrella mode from its D3h equilibrium structure. As was noted earlier the DCS for umbrella mode excited trajectories is shifted slightly towards the forwards region compared with ground state products.…”