Bond selective infrared multiphoton excitation and dissociation of linear monodeuterated acetylene

Abstract

Energetics and spin selectivity in the infrared multiphoton dissociation HN3(X1A')→N2(X1Σ g +)+NH(X3Σ−,a1Δ) AIP Conf.Quantum mechanical simulations of vibrational excitation of monodeuterated linear acetylene ͑HCCD͒ with linearly polarized, frequency-swept, intense but nonionizing infrared laser pulses are performed. The aim is selective dissociation of either H or D atoms by optimal shaping of the laser pulses. We use a discrete variable representation and a compact (Ͻ400 states͒ bright-state expansion to represent the wave function during and after the pulse. Wave packet propagations in the bright-state expansion are at least an order of magnitude faster than discrete variable representation wave packet propagations. This enables optimal-control calculations to find the best parameters for the laser pulses. The dynamics of CH-bond breaking with infrared pulses are very different from the dynamics of CD-bond breaking. This is a direct consequence of CH being the highest-frequency mode in the molecule. Selective CH-bond breaking is possible with two synchronized pulses, the first being quasi-resonant with the ⌬vϭ1 transitions in the CH stretch between vϭ0 and vϭ8, and the second being quasiresonant with ⌬vϭ2 transitions at higher v. H-atom yields as high as 7.7%, with H to D yield ratio as high as 2.1, are demonstrated. Selective CD-bond breaking is possible using a single, subpicosecond, frequency-swept pulse. D-atom yields as high as 3%, or D to H atom yield ratios as high as 3.9, are calculated.

Strong-field optical control of vibrational dynamics: Vibrational Stark effect in planar acetylene

“…Since the 5D direct-product discrete variable representation ͑DVR͒ grid was too large to permit any repetitive calculations to optimize laser pulse sequences, we had to resort to a variant of the ''bright-state'' basis concept 11,12 for such optimizations. As discussed in our previous paper, 13 the onephoton selection rules are A 1 ↔B 2 and A 2 ↔B 1 .…”

“…Using a procedure to be described elsewhere, 15 we also obtained four groups of unpurified ''quasieigenstates'' of A 1 or B 2 symmetry which are similar in spirit to the bright states used in an earlier paper. 12 With the inclusion of these additional eigenstates and quasieigenstates, we obtained an augmented essential-states basis consisting of 89 states of A 1 and B 2 symmetry.…”

“…[1][2][3][4][5][6][7][8][9] Our group has carried out quantum mechanical simulations of the excitation of linear ͑3D͒ HCCH with a few synchronized, linearly polarized, transform-limited, subpicosecond, infrared laser pulses to determine optimal pathways for the selective excitation of the stretching modes in the molecule. [10][11][12] We have demonstrated that it is possible to selectively excite both infrared-active and -inactive vibrational modes of the model linear acetylene using a combination of a few laser pulses.…”

Symmetry-adapted filter diagonalization: Calculation of the vibrational spectrum of planar acetylene from correlation functions

“…[44][45][46][47][48][49][50][51][52][53][54] The most elaborate calculation on this molecule to date involves five active modes, which include two C-H bonds (r 1 ,r 2 ), two Jacobi angles ( 1 , 2 ), and the distance between the two C-H moieties ͑R͒. In a recent work by two of the authors, 54 69 eigenstates were obtained on a ϳ300 000 point grid using the potential of Halonen, Child, and Carter.…”