The dynamics of the Cl+C2H6→HCl(v′,j′)+C2H5 reaction at 0.24 eV: Is ethyl a spectator?

Abstract

State-to-state dynamics of the Cl + CH 3 OH → HCl + CH 2 OH reaction Differential cross section polarization moments: Location of the D-atom transfer in the transition-state region for the reactions Cl+C 2 D 6 →DCl (v ′ =0,J ′ =1)+ C 2 D 5 and Cl+CD 4 →DCl (v ′ =0,J ′ =1)+ CD 3The hydrogen atom abstraction reaction between Cl( 2 P 3/2 ) and ethane has been studied at a mean collision energy of 0.24 eV. The experiments were performed in a coexpansion of molecular chlorine and ethane, with the atomic Cl reactants generated by laser photodissociation of Cl 2 at 355 nm. HCl(vЈ, jЈ) products were detected quantum state selectively using (2ϩ1) resonantly enhanced multiphoton ionization, coupled with velocity-map ion imaging. The ion images were used to determine center-of-mass angular and kinetic energy release distributions. Several analysis methods were employed and have been carefully assessed. It is shown that the single beam experiments can be used with confidence to determine both center-of-mass angular and energy release distributions. For the title reaction the angular distribution is found to be forward peaking, with on average 22% of the available energy channeled into internal excitation of the ethyl coproducts. Possible sources of this internal excitation are discussed.

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

“…In principle our images obtained using the dual molecular beam method measure product velocities in the CM frame, but as was discussed earlier, suffer from undercounting of signal in the backward (θ = 120-180˚) and, to a lesser extent, coworkers deduced that the internal excitation of the radical product was, respectively, ~22% and ~ 30%. 21,22 In CMB studies of the Cl + propane reaction, Blank et al 63 showed that ~40-50% of the available energy was channelled into internal excitation of the propyl radical. Huang et al 27 used CMB methods to investigate the Cl + ethane reaction at four collision energies between 3.2 and 10.4…”

“…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]…”

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

“…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]. Alternative analysis procedures include fitting basis functions to the experimental data, such as in the Legendre moment (LM) method developed by Brouard and coworkers, which has the advantage of allowing for a distribution of internal energies of the co-product [23][24][25].…”

“…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]. Alternative analysis procedures include fitting basis functions to the experimental data, such as in the Legendre moment (LM) method developed by Brouard and coworkers, which has the advantage of allowing for a distribution of internal energies of the co-product [23][24][25].…”