A theoretical analysis of the recent femtosecond photoassociation spectroscopy (FPAS) experiment ... more A theoretical analysis of the recent femtosecond photoassociation spectroscopy (FPAS) experiment on mercury [U. Marvet and M. Dantus, Chem. Phys. Lett. 245, 393 (1995)] is presented. It is shown that when a thermal distribution of diatom collision pairs is excited from a free to a bound electronic state on a time scale shorter than molecular vibration, an ensemble of coherent wave packets is produced. The dynamics of these wave packets created by the photoassociation pulse can be observed by firing a second probe pulse at variable time delays, and the depletion of the first excited bound state by the probe pulse is detected via fluorescence of the remaining population. Simulations of the FPAS experiment, using both wave packet propagation techniques and perturbation theory, clearly show the vibrational dynamics of the photoassociated transients. It is also demonstrated how the FPAS technique may be used as a tool for controlling the energy, impact parameter, and orientation in bimol...
The laser control of reactions in solution has recently been a topic of growing interest. The the... more The laser control of reactions in solution has recently been a topic of growing interest. The theoretical possibility for such control has now been established. This paper investigates two closely related issues regarding potential practical implementation of condensed phase control schemes. A previous study from our group was able to demonstrate control assuming that a laser field coupled only to a reaction coordinate. The assumption that the laser will not couple to the condensed phase environment is a drastic simplification, and we investigate in this paper how relaxing this simplification may affect the possibility of control. To investigate this phenomenon, we study two cases: that of a laser coupled only to a reaction coordinate which is in turn coupled to a ''bath'' mode, as compared to the case in which the laser is coupled both to the reaction coordinate and the environmental mode. In another closely related investigation, we study the effect of uncertainty introduced into the controlling pulse. The exact potential of a chemical reaction in solution cannot be known to perfect accuracy. Our results give insights into the challenges which will face attempts at condensed phase chemical reaction control, and point strongly to the need for adaptive algorithms for laser control pulse generation.
The inverse quantum-mechanical control of molecules is studied using the equation of motion for t... more The inverse quantum-mechanical control of molecules is studied using the equation of motion for the expectation value of an operator. With this method, a requisite external field is obtained to track exactly a prescribed molecular objective expectation value as a function of time. Applications to diatomic and polyatomic molecules are formulated. While the method is directly applicable as a test of physical intuition, it can in principle be used to design fields for specific objectives including reactive selectivity. Results are presented for position and energy tracking in the hydrogen fluoride molecular system. The numerical calculations show that seemingly benign objective tracks may give rise to singularities in the field. However, these singularities do not present problems in the evolution of the dynamical quantities and instead provide useful hints for designing robust fields.
We examine the applicability of variations of exact tracking, including asymptotic tracking, stat... more We examine the applicability of variations of exact tracking, including asymptotic tracking, state-dependent trajectory tracking, and competitive tracking, for the problem of generating feasible external laser fields for control of classically modeled molecular motion via ...
Excitation of molecular hydrogen has been studied in 1.8-keV collisions with molecular projectile... more Excitation of molecular hydrogen has been studied in 1.8-keV collisions with molecular projectile ions H+2, N+2, CO+, O+2, and CO+2 by means of energy-loss spectrometry using a high-resolution ion translational-energy spectrometer. Excitation of the target H2 is observed only in the case of collisions with H+2. Oscillator strengths for electronic transitions to various electronic states are determined by simulating the
Abstract A new scheme for controlling photodissociation through preparation of a variationally op... more Abstract A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on ...
An optimization procedure for producing selective excitation of molecules undergoing stochastic d... more An optimization procedure for producing selective excitation of molecules undergoing stochastic dephasing collisions is presented. The collisional effects are incorporated by propagating the Schrodinger equation with random perturbations. The optimization procedure utilizes gradients of the perturbation‐averaged physical objective with respect to the laser field parameters; we demonstrate on a model problem that very few averages over collisional events suffice to yield converged results. Therefore, this method is computationally efficient because large averaging of dynamical simulations is not necessary. These results show the viability of the optimal control procedure for application to controlling chemical reactions in solution.
Simulations of the quantum dynamics of the HF molecule immersed in a field of five overlapping, i... more Simulations of the quantum dynamics of the HF molecule immersed in a field of five overlapping, intense, linearly polarized, infrared laser pulses of subpicosecond duration are performed. The HF molecule, initially in its ground state, is modeled as a rotating ...
An iterative optimization algorithm for designing laser fields to control molecular motion which ... more An iterative optimization algorithm for designing laser fields to control molecular motion which utilizes laboratory input (test fields) and output (resulting product yields) information is proposed. Laboratory uncertainties such as laser field noise and limited precision in the ...
Initial state laser control of curve‐crossing reactions using the RayleighRitz variational proce... more Initial state laser control of curve‐crossing reactions using the RayleighRitz variational procedure. [The Journal of Chemical Physics 104, 7045 (1996)]. Peter Gross, Ashish K. Gupta, Deepa B. Bairagi, Manoj K. Mishra. Abstract. ...
A theoretical analysis of the recent femtosecond photoassociation spectroscopy (FPAS) experiment ... more A theoretical analysis of the recent femtosecond photoassociation spectroscopy (FPAS) experiment on mercury [U. Marvet and M. Dantus, Chem. Phys. Lett. 245, 393 (1995)] is presented. It is shown that when a thermal distribution of diatom collision pairs is excited from a free to a bound electronic state on a time scale shorter than molecular vibration, an ensemble of coherent wave packets is produced. The dynamics of these wave packets created by the photoassociation pulse can be observed by firing a second probe pulse at variable time delays, and the depletion of the first excited bound state by the probe pulse is detected via fluorescence of the remaining population. Simulations of the FPAS experiment, using both wave packet propagation techniques and perturbation theory, clearly show the vibrational dynamics of the photoassociated transients. It is also demonstrated how the FPAS technique may be used as a tool for controlling the energy, impact parameter, and orientation in bimol...
The laser control of reactions in solution has recently been a topic of growing interest. The the... more The laser control of reactions in solution has recently been a topic of growing interest. The theoretical possibility for such control has now been established. This paper investigates two closely related issues regarding potential practical implementation of condensed phase control schemes. A previous study from our group was able to demonstrate control assuming that a laser field coupled only to a reaction coordinate. The assumption that the laser will not couple to the condensed phase environment is a drastic simplification, and we investigate in this paper how relaxing this simplification may affect the possibility of control. To investigate this phenomenon, we study two cases: that of a laser coupled only to a reaction coordinate which is in turn coupled to a ''bath'' mode, as compared to the case in which the laser is coupled both to the reaction coordinate and the environmental mode. In another closely related investigation, we study the effect of uncertainty introduced into the controlling pulse. The exact potential of a chemical reaction in solution cannot be known to perfect accuracy. Our results give insights into the challenges which will face attempts at condensed phase chemical reaction control, and point strongly to the need for adaptive algorithms for laser control pulse generation.
The inverse quantum-mechanical control of molecules is studied using the equation of motion for t... more The inverse quantum-mechanical control of molecules is studied using the equation of motion for the expectation value of an operator. With this method, a requisite external field is obtained to track exactly a prescribed molecular objective expectation value as a function of time. Applications to diatomic and polyatomic molecules are formulated. While the method is directly applicable as a test of physical intuition, it can in principle be used to design fields for specific objectives including reactive selectivity. Results are presented for position and energy tracking in the hydrogen fluoride molecular system. The numerical calculations show that seemingly benign objective tracks may give rise to singularities in the field. However, these singularities do not present problems in the evolution of the dynamical quantities and instead provide useful hints for designing robust fields.
We examine the applicability of variations of exact tracking, including asymptotic tracking, stat... more We examine the applicability of variations of exact tracking, including asymptotic tracking, state-dependent trajectory tracking, and competitive tracking, for the problem of generating feasible external laser fields for control of classically modeled molecular motion via ...
Excitation of molecular hydrogen has been studied in 1.8-keV collisions with molecular projectile... more Excitation of molecular hydrogen has been studied in 1.8-keV collisions with molecular projectile ions H+2, N+2, CO+, O+2, and CO+2 by means of energy-loss spectrometry using a high-resolution ion translational-energy spectrometer. Excitation of the target H2 is observed only in the case of collisions with H+2. Oscillator strengths for electronic transitions to various electronic states are determined by simulating the
Abstract A new scheme for controlling photodissociation through preparation of a variationally op... more Abstract A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on ...
An optimization procedure for producing selective excitation of molecules undergoing stochastic d... more An optimization procedure for producing selective excitation of molecules undergoing stochastic dephasing collisions is presented. The collisional effects are incorporated by propagating the Schrodinger equation with random perturbations. The optimization procedure utilizes gradients of the perturbation‐averaged physical objective with respect to the laser field parameters; we demonstrate on a model problem that very few averages over collisional events suffice to yield converged results. Therefore, this method is computationally efficient because large averaging of dynamical simulations is not necessary. These results show the viability of the optimal control procedure for application to controlling chemical reactions in solution.
Simulations of the quantum dynamics of the HF molecule immersed in a field of five overlapping, i... more Simulations of the quantum dynamics of the HF molecule immersed in a field of five overlapping, intense, linearly polarized, infrared laser pulses of subpicosecond duration are performed. The HF molecule, initially in its ground state, is modeled as a rotating ...
An iterative optimization algorithm for designing laser fields to control molecular motion which ... more An iterative optimization algorithm for designing laser fields to control molecular motion which utilizes laboratory input (test fields) and output (resulting product yields) information is proposed. Laboratory uncertainties such as laser field noise and limited precision in the ...
Initial state laser control of curve‐crossing reactions using the RayleighRitz variational proce... more Initial state laser control of curve‐crossing reactions using the RayleighRitz variational procedure. [The Journal of Chemical Physics 104, 7045 (1996)]. Peter Gross, Ashish K. Gupta, Deepa B. Bairagi, Manoj K. Mishra. Abstract. ...
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Papers by Peter Gross