Dynamics for the Cl+C2H6→HCl+C2H5 reaction examined through state-specific angular distributions

Abstract

Photolysis of Cl 2 initiates the title reaction at a sharply defined collision energy of 0.24Ϯ0.03 eV. Nascent product rotational state distributions for HCl ͑vϭ0͒ are determined using resonance enhanced multiphoton ionization ͑REMPI͒, center-of-mass scattering distributions are measured by the core-extraction technique, and the average internal energy of the C 2 H 5 product is deduced from the dependence of the core-extracted signal on the photolysis polarization. The HCl product has little rotational excitation, but the scattering distribution is nearly isotropic. Although seemingly contradictory, both of these features can be accounted for by using the simple line-of-centers model presented to explain earlier results for the ClϩCH 4 reaction. In contrast to the ClϩCH 4 reaction, the data suggest that the ClϩC 2 H 6 reaction proceeds through a loosely constrained transition-state geometry. The reactions of atomic chlorine with ethane, C 2 H 6 , and perdeuteroethane, C 2 D 6 , yield virtually identical results. These findings, along with the low energy deposited by the reaction into the ethyl product ͑200Ϯ120 cm Ϫ1 ͒, demonstrate that the alkyl fragment acts largely as a spectator in this hydrogen abstraction reaction.

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

“…In an early dynamical study, Flynn and co-workers employed infra-red absorption spectroscopy of the DCl products of reaction of Cl atoms with d 12 -cyclohexane, 3 but the subsequent combination of resonance enhanced multi-photon ionization (REMPI) or vacuum ultraviolet (VUV) ionization with velocity resolution of reaction products has proved most informative. 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.…”

“…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 .…”

Imaging the Dynamics of Reactions between Cl Atoms and the Cyclic Ethers Oxirane and Oxetane

“…The extracted zeroth-and second-order experimental Legendre moments of the HCl(V′ ) 0, J′ ) 2) products from the Cl + c-C 2 H 4 O reaction are shown in Figure 4, along with fits using the (3,5) set of calculated basis functions. There is some contaminant HCl present at very low speeds, but the fitting was otherwise satisfactory.…”

“…Basis functions constructed from (3,3), (4,4), and (3,5) sets of Legendre functions were tested for the fitting. Analysis was performed using basis functions that assumed each of the following three possibilities: (i) abstraction of H atoms only from R-C atoms; (ii) abstraction only from -C atoms; (iii) abstraction from both R-and -C atoms with adjustable weights.…”

Velocity map imaging of the dynamics of the CH3+ HCl → CH4+ Cl reaction using a dual molecular beam method

“…Zare and coworkers [19] and Brouard and coworkers [20] were instrumental in the development and application of these PHOTOLOC experiments, so-called because in the photoinitiated scheme, the product lab frame speed distribution P(v) can be related to the centre-of-mass (CM) frame angular scattering distribution (which is proportional to the DCS) by a simple law of cosines relationship Direct inversion of the P(v) distribution to obtain the DCS only applies unambiguously for reactions where the undetected co-product (C in reaction (2)) is an atom formed with a single well-defined internal energy. In polyatomic reactions, multiple internal energy states of the radical or molecular co-product are usually populated and direct data inversion either requires the assumption that the internal energy is zero [21], or an average value is deduced from analysis that incorporates the lab frame anisotropy [22]. Any assumptions made about the internal energy will have an effect on the returned DCS, with the tendency to overestimate the sideways scattered component [23].…”