Chemistry in strong laser fields: An example from methyl iodide photodissociation

Audrey Dell Hammerich, Ronnie Kosloff, Mark A Ratner

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

Time-dependent quantum-mechanical theories and simulations provide a clear and intuitive description of molecular processes. Due to ensuing simplification of the theory and the generally employed numerical algorithms, the vast majority of these treatments are based upon perturbation theory. Especially in light of the current level of experimental sophistication, with experiments being realized which are influenced by the spectral, temporal, and spatial shape of the laser pulse, it is important to move beyond treatments limited to weak fields or idealized δ-function wave forms. Various methods to examine the results of high-field simulations are presented. All of the techniques are shown to have the familiar linear response form in the weak-field limit. In a time-dependent framework the difference between the linear and nonlinear response expressions can be seen from expectation values over stationary versus nonstationary states. The high-field photodissociation of methyl iodide illustrates this approach. Methyl iodide represents a physical system well suited for examining the effects of such exciting laser-field characteristics as strength, linewidth, and frequency upon the photodissociation dynamics. Its dissociation occurs upon coupled repulsive excited electronic potential-energy surfaces which have recently been revised to fit the most current experimental data. The effect of the surface intersection has previously been typically studied by examining the branching and the internal state distributions of the products in the two channels as a function of excitation frequency only. The collinear photodissociation dynamics is examined using a numerically exact time-dependent quantum-mechanical method. The equations of motion for the amplitudes upon the ground and two coupled excited electronic surfaces, explicitly incorporating the laser field, are integrated by a scheme which employs a low-order polynomial approximation to the evolution operator. The effects of the three field characteristics upon the branching ratio and internal state distributions of the products and the spectroscopy of the process are delineated. The course of the photodissociation dynamics is shown to be affected by these characteristics. The results demonstrate the causal connections between the pulse shape and the resulting photoprocesses. Practical manifestations of strong fields (power broadening, subthreshold absorption, higher harmonic generation, emission shaping of the ground state, temporal development) are stressed.

Original languageEnglish
Pages (from-to)6410-6431
Number of pages22
JournalJournal of Chemical Physics
Volume97
Issue number9
Publication statusPublished - 1992

Fingerprint

Photodissociation
photodissociation
iodides
chemistry
Lasers
lasers
Polynomial approximation
Potential energy surfaces
products
Harmonic generation
Wave functions
pulses
simplification
electronics
Linewidth
intersections
Ground state
Equations of motion
Mathematical operators
Laser pulses

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Chemistry in strong laser fields : An example from methyl iodide photodissociation. / Dell Hammerich, Audrey; Kosloff, Ronnie; Ratner, Mark A.

In: Journal of Chemical Physics, Vol. 97, No. 9, 1992, p. 6410-6431.

Research output: Contribution to journalArticle

Dell Hammerich, Audrey ; Kosloff, Ronnie ; Ratner, Mark A. / Chemistry in strong laser fields : An example from methyl iodide photodissociation. In: Journal of Chemical Physics. 1992 ; Vol. 97, No. 9. pp. 6410-6431.
@article{7d090d2934c948f58a8e9c5b01cf43b8,
title = "Chemistry in strong laser fields: An example from methyl iodide photodissociation",
abstract = "Time-dependent quantum-mechanical theories and simulations provide a clear and intuitive description of molecular processes. Due to ensuing simplification of the theory and the generally employed numerical algorithms, the vast majority of these treatments are based upon perturbation theory. Especially in light of the current level of experimental sophistication, with experiments being realized which are influenced by the spectral, temporal, and spatial shape of the laser pulse, it is important to move beyond treatments limited to weak fields or idealized δ-function wave forms. Various methods to examine the results of high-field simulations are presented. All of the techniques are shown to have the familiar linear response form in the weak-field limit. In a time-dependent framework the difference between the linear and nonlinear response expressions can be seen from expectation values over stationary versus nonstationary states. The high-field photodissociation of methyl iodide illustrates this approach. Methyl iodide represents a physical system well suited for examining the effects of such exciting laser-field characteristics as strength, linewidth, and frequency upon the photodissociation dynamics. Its dissociation occurs upon coupled repulsive excited electronic potential-energy surfaces which have recently been revised to fit the most current experimental data. The effect of the surface intersection has previously been typically studied by examining the branching and the internal state distributions of the products in the two channels as a function of excitation frequency only. The collinear photodissociation dynamics is examined using a numerically exact time-dependent quantum-mechanical method. The equations of motion for the amplitudes upon the ground and two coupled excited electronic surfaces, explicitly incorporating the laser field, are integrated by a scheme which employs a low-order polynomial approximation to the evolution operator. The effects of the three field characteristics upon the branching ratio and internal state distributions of the products and the spectroscopy of the process are delineated. The course of the photodissociation dynamics is shown to be affected by these characteristics. The results demonstrate the causal connections between the pulse shape and the resulting photoprocesses. Practical manifestations of strong fields (power broadening, subthreshold absorption, higher harmonic generation, emission shaping of the ground state, temporal development) are stressed.",
author = "{Dell Hammerich}, Audrey and Ronnie Kosloff and Ratner, {Mark A}",
year = "1992",
language = "English",
volume = "97",
pages = "6410--6431",
journal = "Journal of Chemical Physics",
issn = "0021-9606",
publisher = "American Institute of Physics Publising LLC",
number = "9",

}

TY - JOUR

T1 - Chemistry in strong laser fields

T2 - An example from methyl iodide photodissociation

AU - Dell Hammerich, Audrey

AU - Kosloff, Ronnie

AU - Ratner, Mark A

PY - 1992

Y1 - 1992

N2 - Time-dependent quantum-mechanical theories and simulations provide a clear and intuitive description of molecular processes. Due to ensuing simplification of the theory and the generally employed numerical algorithms, the vast majority of these treatments are based upon perturbation theory. Especially in light of the current level of experimental sophistication, with experiments being realized which are influenced by the spectral, temporal, and spatial shape of the laser pulse, it is important to move beyond treatments limited to weak fields or idealized δ-function wave forms. Various methods to examine the results of high-field simulations are presented. All of the techniques are shown to have the familiar linear response form in the weak-field limit. In a time-dependent framework the difference between the linear and nonlinear response expressions can be seen from expectation values over stationary versus nonstationary states. The high-field photodissociation of methyl iodide illustrates this approach. Methyl iodide represents a physical system well suited for examining the effects of such exciting laser-field characteristics as strength, linewidth, and frequency upon the photodissociation dynamics. Its dissociation occurs upon coupled repulsive excited electronic potential-energy surfaces which have recently been revised to fit the most current experimental data. The effect of the surface intersection has previously been typically studied by examining the branching and the internal state distributions of the products in the two channels as a function of excitation frequency only. The collinear photodissociation dynamics is examined using a numerically exact time-dependent quantum-mechanical method. The equations of motion for the amplitudes upon the ground and two coupled excited electronic surfaces, explicitly incorporating the laser field, are integrated by a scheme which employs a low-order polynomial approximation to the evolution operator. The effects of the three field characteristics upon the branching ratio and internal state distributions of the products and the spectroscopy of the process are delineated. The course of the photodissociation dynamics is shown to be affected by these characteristics. The results demonstrate the causal connections between the pulse shape and the resulting photoprocesses. Practical manifestations of strong fields (power broadening, subthreshold absorption, higher harmonic generation, emission shaping of the ground state, temporal development) are stressed.

AB - Time-dependent quantum-mechanical theories and simulations provide a clear and intuitive description of molecular processes. Due to ensuing simplification of the theory and the generally employed numerical algorithms, the vast majority of these treatments are based upon perturbation theory. Especially in light of the current level of experimental sophistication, with experiments being realized which are influenced by the spectral, temporal, and spatial shape of the laser pulse, it is important to move beyond treatments limited to weak fields or idealized δ-function wave forms. Various methods to examine the results of high-field simulations are presented. All of the techniques are shown to have the familiar linear response form in the weak-field limit. In a time-dependent framework the difference between the linear and nonlinear response expressions can be seen from expectation values over stationary versus nonstationary states. The high-field photodissociation of methyl iodide illustrates this approach. Methyl iodide represents a physical system well suited for examining the effects of such exciting laser-field characteristics as strength, linewidth, and frequency upon the photodissociation dynamics. Its dissociation occurs upon coupled repulsive excited electronic potential-energy surfaces which have recently been revised to fit the most current experimental data. The effect of the surface intersection has previously been typically studied by examining the branching and the internal state distributions of the products in the two channels as a function of excitation frequency only. The collinear photodissociation dynamics is examined using a numerically exact time-dependent quantum-mechanical method. The equations of motion for the amplitudes upon the ground and two coupled excited electronic surfaces, explicitly incorporating the laser field, are integrated by a scheme which employs a low-order polynomial approximation to the evolution operator. The effects of the three field characteristics upon the branching ratio and internal state distributions of the products and the spectroscopy of the process are delineated. The course of the photodissociation dynamics is shown to be affected by these characteristics. The results demonstrate the causal connections between the pulse shape and the resulting photoprocesses. Practical manifestations of strong fields (power broadening, subthreshold absorption, higher harmonic generation, emission shaping of the ground state, temporal development) are stressed.

UR - http://www.scopus.com/inward/record.url?scp=3342882995&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=3342882995&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:3342882995

VL - 97

SP - 6410

EP - 6431

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 9

ER -