Stereodynamic Imaging of Bromine Atomic Photofragments Eliminated from 1-Bromo-2-methylbutane Oriented via Hexapole State Selector

Abstract

Both single-laser and two-laser experiments were conducted to look into the ion-imaging of Br*( 2 P1/2) and Br( 2 P3/2) photo-fragmented from 1-bromo-2-methylbutane in the range 232-240 nm via a detection scheme of (2+1) resonance-enhanced multiphoton ionization. The angular analysis of these photofragment distributions yields the anisotropy parameter β = 1.88 ± 0.06 for the Br* excited state which arises from a parallel transition, while β = 0.63 ± 0.09 for the Br ground state indicates the contribution from both a perpendicular transition and a non-adiabatic transition. When a hexapole coupled with an orienting field was implemented, the parent molecules are spatially oriented to yield an orientation efficiency |<cosθ>| of 0.15. Besides the χ angle between the recoil velocity v and the transition dipole moment μ, orienting molecules allows for the evaluation of the angle α between v and the permanent molecular dipole moment d. The angular analysis of Br * photofragment distribution yields χ to be 11.5° and α in the range from 160° to 180° with weak dependency. In the two-laser experiments, the angular anisotropy of Br photofragment distribution was found to be smaller (0.38 ± 0.10) when the photolysis wavelength was red-shifted to 240 nm, suggesting the increasing contributions from perpendicular transitions.

UV Photodissociation of Halothane in a Focused Molecular Beam: Space-Speed Slice Imaging of Competitive Bond Breaking into Spin–Orbit-Selected Chlorine and Bromine Atoms

“…Subsequent to the excitation at 234 nm determining a transition to the n σ*­(C–Br) surface, the following picture emerges: a nonbonding electron of Br is promoted to the σ* orbital, followed by a sudden rupture of the C–Br bond yielding both Br and Br* atoms, which bear a considerable amount of the release of the available translational energy, characterized by a Gaussian with a large β value. We have extensively investigated previously, in the Taiwan set-up, the formation mechanism of Br and Br* atoms in the photodissociation of 2-bromobutane and 1-bromo-2-methylbutane, analyzing the vector correlation measured by hexapole-oriented molecular beams: all of these results are consistent with the mechanism of bromine atoms being formed through a direct dissociation path leading to sharply distributed scattering, peaked in the θ = 0 direction. Smaller values of β for production of the ground state of Br are attributed to the mixing of a parallel transition, 3 Q 1 , and of a nonadiabatic transition from the perpendicular surfaces, 3 Q 0 and 1 Q 1 .…”

A vector correlation study using a hexapole-oriented molecular beam: photodissociation dynamics of oriented isohaloethane

“…These results are similar to those reported in our previous studies concerning the photodissociation of halothane and other molecules. 23,29–31 The total kinetic energy release for the Br atom was slightly higher than that for Br* because some of the available energy was spent on electronic excitation for the latter product. A similar tendency was observed in the case of halothane photodissociation.…”

“…This finding clearly indicates that the molecules were oriented in the laboratory frame. 30,31 To quantitatively examine the effect of orientation in the molecular beam, the TOF spectrum was simulated as indicated by the solid line. In the case of an oriented beam, deconvolution requires consideration of the orientation probability distribution function, D (cos δ ), as a function of δ as expressed in eqn (1).…”

“…In our previous work, we demonstrated that some conformers could be focused using a hexapole electric field and discussed the possibility of applying this to conformer selection. 31,33,34 Although the contributing conformers cannot be identified at present, several conformers are expected to be present in the focused beam. The disagreement between the vector correlation and the anisotropic parameter may be attributable to the contribution of these conformers.…”

Pattern analysis of the impact‐parameter dependent trajectories for the H + H2 exchange reaction at T = 3 and 300 K: A characteristic propensity for reactive versus nonreactive trajectories found in the time‐dependent interaction potential and a roaming‐like libration motion at cold temperature

“…Thus, the rotational degree-of-freedom basically due to the orbital angular momentum at nonzero impact-parameter collisions would lead to collision dynamics more complex and fruitful. [55][56][57][58][59] The present study aims at extending the idea of two dimensional (2D) Polanyi rule to three dimensional (3D) one where we explicitly consider rotational degree-of-freedom.…”