State-resolved reactive scattering by slice imaging: A new view of the Cl+C2H6 reaction

Abstract

We present state-resolved crossed beam scattering results for the reaction Cl+C2H6-->HCl+C2H5, obtained using direct current slice imaging. The HCl (v=0,J=2) image, recorded at a collision energy of 6.7+/-0.6 kcalmol, shows strongly coupled angular and translational energy distributions revealing features of the reaction not seen in previous studies. The overall distribution is mainly forward scattered with respect to the Cl beam, with a translational energy distribution peaking near the collision energy. However, there is a substantial backscattered contribution that is very different. It shows a sharp peak at 8.0 kcalmol, but extends to much lower energy, implying substantial internal excitation in the ethyl radical coproduct. These results provide new insight into the reaction, and they are considered in terms of alternative models of the dynamics. This work represents the first genuine crossed-beam study in which a product other than the methyl radical was detected with quantum state specificity, showing the promise of the approach generally for high resolution state-resolved reactive scattering.

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]…”

Reaction Dynamics of Phenyl Radicals in Extreme Environments: A Crossed Molecular Beam Study

“…In principle, both reactant beams can be prepared in well-defined quantum states before they cross at a specific collision energy under single collision conditions. The products can be monitored via spectroscopic detection schemes such as laser-induced fluorescence (LIF) 40 or Rydberg tagging, 41 via ion imaging probes, 42,43 or via a quadrupole mass spectrometric detector (QMS) with universal electron impact ionization or photoionization coupled to a mass spectrometric device. Here, the crossed molecular beam method with mass spectrometric detection presents the most versatile technique to study these elementary reactions thus permitting the elucidation of the chemical dynamics and, in the case of polyatomic reactions, the primary products.…”

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

“…Multiplexing methods such as velocity map imaging (VMI) that detect flux into all scattering angles simultaneously are clearly advantageous, but it is only relatively recently that crossed-beam experiments in conjunction with VMI techniques and state-specific detection have been possible for polyatomic molecule reactions. Thus, only a few systems have been studied in this way, including reactions of Cl, F and O atoms with alkanes (most notably methane) [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and the F atom reaction with silane [18]. Experimental strategies that have been developed to overcome the problem of low signal levels include single-beam co-expansion (commonly referred to as PHOTOLOC) and dual-beam techniques; both methods employ a photoinitiation step in which photodissociation of a precursor molecule AX starts the following reaction sequence: AX + hv → A + X…”