Abstract:We perform quantum mechanical simulations of vibrational excitation of planar (5D) acetylene (HCCH) with linearly polarized, intense but nonionizing, infrared laser pulses, exploring one particular pathway for exciting the HCCH molecule into a CC-stretching state via the fundamental excitation in a two-pulse scheme. We optimize the pulse widths, time centers, and carrier frequencies of the two pulses to achieve the maximal projection onto the target CC-stretching state, (0,3,0,0,0) A1, subject to penalties rel… Show more
“…The proportionality of R(11) IR−UV DR background signal strength to IR PUMP power is also inconsistent with a possible CIQCB mechanism involving Stark-induced mixing of rovibrational states of the (1 0 3 0 0) 0 submanifold, effectively induced by the electric field of the IR PUMP laser. (In contrast, we note studies of the vibrational Stark effect in C 2 H 2 , in which the transition strength of nominally forbidden rovibrational transitions, induced by laser field-induced Stark mixing, is shown to vary in a nonlinear fashion with the strength of the applied laser field.) 10 R(11) IR−UV DR background signal strength for C 2 H 2 ( P = 0.20 Torr, t = 550 ns, z = 1.8) plotted as a function of IR PUMP power.…”
The 4nu(CH) rovibrational manifold around 12 700 cm(-1) in the electronic ground state, X, of acetylene (C2H2) is monitored by time-resolved infrared-ultraviolet double-resonance (IR-UV DR) spectroscopy. An IR laser pulse initially prepares rotational J states, associated with the "IR-bright" (nu1 + 3nu3) or (1 0 3 0 0)0 vibrational combination level, and subsequent collision-induced state-to-state energy transfer is probed by UV laser-induced fluorescence. Anharmonic, l-resonance, and Coriolis couplings affect the J states of interest, resulting in a congested rovibrational manifold that exhibits complex intramolecular dynamics. In preceding papers in this series, we have described three complementary forms of the IR-UV DR experiment (IR-scanned, UV-scanned, and kinetic) on collision-induced rovibrational satellites, comprising both regular even-DeltaJ features and unexpected odd-DeltaJ features. This paper examines an unusual collision-induced quasi-continuous background (CIQCB) effect that is apparently ubiquitous, accompanying regular even-DeltaJ rovibrational energy transfer and accounting for much of the observed collision-induced odd-DeltaJ satellite structure; certain IR-bright (1 0 3 0 0)0 rovibrational states (e.g., J = 12) are particularly prominent in this regard. We examine the mechanism of this CIQCB phenomenon in terms of a congested IR-dark rovibrational manifold that is populated by collisional transfer from the nearly isoenergetic IR-bright (1 0 3 0 0)0 submanifold.
“…The proportionality of R(11) IR−UV DR background signal strength to IR PUMP power is also inconsistent with a possible CIQCB mechanism involving Stark-induced mixing of rovibrational states of the (1 0 3 0 0) 0 submanifold, effectively induced by the electric field of the IR PUMP laser. (In contrast, we note studies of the vibrational Stark effect in C 2 H 2 , in which the transition strength of nominally forbidden rovibrational transitions, induced by laser field-induced Stark mixing, is shown to vary in a nonlinear fashion with the strength of the applied laser field.) 10 R(11) IR−UV DR background signal strength for C 2 H 2 ( P = 0.20 Torr, t = 550 ns, z = 1.8) plotted as a function of IR PUMP power.…”
The 4nu(CH) rovibrational manifold around 12 700 cm(-1) in the electronic ground state, X, of acetylene (C2H2) is monitored by time-resolved infrared-ultraviolet double-resonance (IR-UV DR) spectroscopy. An IR laser pulse initially prepares rotational J states, associated with the "IR-bright" (nu1 + 3nu3) or (1 0 3 0 0)0 vibrational combination level, and subsequent collision-induced state-to-state energy transfer is probed by UV laser-induced fluorescence. Anharmonic, l-resonance, and Coriolis couplings affect the J states of interest, resulting in a congested rovibrational manifold that exhibits complex intramolecular dynamics. In preceding papers in this series, we have described three complementary forms of the IR-UV DR experiment (IR-scanned, UV-scanned, and kinetic) on collision-induced rovibrational satellites, comprising both regular even-DeltaJ features and unexpected odd-DeltaJ features. This paper examines an unusual collision-induced quasi-continuous background (CIQCB) effect that is apparently ubiquitous, accompanying regular even-DeltaJ rovibrational energy transfer and accounting for much of the observed collision-induced odd-DeltaJ satellite structure; certain IR-bright (1 0 3 0 0)0 rovibrational states (e.g., J = 12) are particularly prominent in this regard. We examine the mechanism of this CIQCB phenomenon in terms of a congested IR-dark rovibrational manifold that is populated by collisional transfer from the nearly isoenergetic IR-bright (1 0 3 0 0)0 submanifold.
“…When the stretches are introduced, the stretch-bend problem in the plane is essentially as complicated as the threedimensional pure bends problem: both involve three nonlinear resonance coupling terms. Furthermore, the planar model has been of interest in itself, in model studies of coherent control [12]. Lastly, a better understanding of the stretch-bend problem, even in a simplified planar model, is of pressing interest, because of the possible involvement of the stretches in the acetylene-vinylidene isomerization process.…”
Abstract.A diabatic correlation diagram procedure is used to classify energy and intensity patterns in a planar model for coupled stretches and bends of acetylene using an effective spectroscopic fitting Hamiltonian. Analysis with polyad phase spheres accounts for the observed patterns in terms of classical phase space structure and bifurcations of the normal modes.PACS. 31.15.-p Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations)
“…An early account was given by Billing and Henriksen, who developed a semiclassical approach to the photofragmentation of polyatomics. More recent examples include the study of excitation of the C−C stretching vibration in planar acetylene, focusing on the influence of Fermi resonances and the vibrational Stark effect. This five-dimensional treatment was made possible by exploring the idea of essential states .…”
The performance of locally generated driving fields in the case of strong mode competition in two-dimensional
models of the title reaction is investigated. The simulations are based on an all-Cartesian reaction surface
Hamiltonian derived from ab initio quantum chemistry data. Here the one-dimensional reaction coordinate is
defined by the Co−CO distance and motions of the HCo(CO)3 fragment are described in the harmonic
approximation. The influence of two substrate normal modes is investigated in detail. First, we consider the
high-frequency H−Co stretching vibration, whose presence is shown to give no problem for driving the
reaction coordinate. Second, we focus on a low-frequency umbrella-type mode involving the equatorial
carbonyls. This mode provides a challenge to the method because of resonance and dipole gradient effects.
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