The selective control of O-H/O-D bond dissociation in reduced dimensionality model of HOD molecule has been explored through IR+UV femtosecond pulses. The IR pulse has been optimized using simulated annealing stochastic approach to maximize population of a desired low quanta vibrational state. Since those vibrational wavefunctions of the ground electronic states are preferentially localized either along the O-H or O-D mode, the femtosecond UV pulse is used only to transfer vibrationally excited molecule to the repulsive upper surface to cleave specific bond, O-H or O-D. While transferring from the ground electronic state to the repulsive one, the optimization of the UV pulse is not necessarily required except specific case. The results so obtained are analyzed with respect to time integrated flux along with contours of time evolution of probability density on excited potential energy surface. After preferential excitation from [line]0, 0> ([line]m, n> stands for the state having m and n quanta of excitations in O-H and O-D mode, respectively) vibrational level of the ground electronic state to its specific low quanta vibrational state ([line]1, 0> or [line]0, 1> or [line]2, 0> or [line]0, 2>) by using optimized IR pulse, the dissociation of O-D or O-H bond through the excited potential energy surface by UV laser pulse appears quite high namely, 88% (O-H ; [line]1, 0>) or 58% (O-D ; [line]0, 1>) or 85% (O-H ; [line]2, 0>) or 59% (O-D ; [line]0, 2>). Such selectivity of the bond breaking by UV pulse (if required, optimized) together with optimized IR one is encouraging compared to the normal pulses.
We propose a strategy of using a stochastic optimization technique, namely, simulated annealing to design optimum laser pulses (both IR and UV) to achieve greater fluxes along the two dissociating channels (O(18) + O(16)O(16) and O(16) + O(16)O(18)) in O(16)O(16)O(18) molecule. We show that the integrated fluxes obtained along the targeted dissociating channel is larger with the optimized pulse than with the unoptimized one. The flux ratios are also more impressive with the optimized pulse than with the unoptimized one. We also look at the evolution contours of the wavefunctions along the two channels with time after the actions of both the IR and UV pulses and compare the profiles for unoptimized (initial) and optimized fields for better understanding the results that we achieve. We also report the pulse parameters obtained as well as the final shapes they take.
Vibrational excitation cross-sections σ ν f ←ν i (E) in resonant e-F 2 and HCl scattering are calculated from transition matrix elements T ν f ←ν i (E) obtained using Fourier transform of the cross correlation function φ ν f (R) | ν i (R, t) where ν i (R, t) ≈ e −i H AB − (R)t φ ν i (R). Time evolution under the influence of the resonance anionic Hamiltonian H AB-(AB=F 2 /HCl) is effected using Lanczos reduction technique followed by fast Fourier transform and the target (AB) vibrational eigenfunctions φ ν i (R) and φ ν f (R) are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curve of the neutral target. The resulting vibrational excitation cross-sections provide reasonable agreement with experimental and other theoretical results.
The 2 P g N À 2 and 3 R À NO À resonances in electron-N 2 and NO collisions have been treated using both nuclear and electronic degrees of freedom and a two-dimensional (2D) time dependent wave packet approach to ascertain the importance of nonlocality in electron-nuclear interaction. The results so obtained are compared with vibrational excitation crosssections obtained experimentally and those from other theoretical/numerical approaches using 1D local complex potential, 2D model with a combination of the exterior complex scaling method and a finite-element implementation of the discrete-variable representation. The results obtained provide detailed insight into the nuclear dynamics induced by electronmolecule collision and reveal that while for resonant excitation of lower vibrational modes, the nonlocal effect may not be as critical but importance of nonlocal effects may increase with increase in quanta of resonant vibrational excitation.
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