Quantum mechanical simulations of vibrational excitation of monodeuterated linear acetylene (HCCD) 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 (<400 states) 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 Δv= 1 transitions in the CH stretch between v = 0 and v = 8, and the second being quasiresonant with Δv = 2 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.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry