### Abstract

The full nine-dimensional potential energy surfaces (PESs) of the ^{3}Q_{0} and ^{1}Q_{1} states of CH_{3}I have been calculated with the ab initio contracted spin-orbit configuration interaction method. The results are fitted to three diabatic potential terms and their couplings as functions of all the internal degrees of freedom. The transition dipole at the Franck-Condon region has also been calculated. Surface hopping quasiclassical trajectory calculations on these potential energy surfaces have been performed to examine the photodissociation dynamics of both CH_{3}I and CD_{3}I in the A-continuum. The results are in general good agreement with the recent experimental findings. The reasonable I*/(I*+I) branching ratio can be obtained with these PESs when the contribution of direct transition to the ^{1}Q_{1} state is considered. The rotational distribution of the CH_{3} and CD_{3} fragments and its I*/(I*+I)-channel selectivity are determined by the shape of the PESs with respect to the bending angle outside the conical intersection region. The vibrational distribution of umbrella mode is closely related to the shape of PESs for the umbrella angle; the sudden switch of reaction coordinate from ^{3}Q_{0} to ^{1}Q_{1} at the conical intersection is the origin of vibrational excitation in the I* channel. The larger umbrella excitation of the CD_{3} fragment in both I and I* channels, in comparison with the CH_{3} fragment, is related to the larger separation of the reaction coordinate from the Franck-Condon geometry. The symmetric stretching energy increases during the dissociation, which is related to the shape of PESs with respect to this coordinate, and the excitation of symmetric stretching mode seems to be possible.

Original language | English |
---|---|

Pages (from-to) | 9783-9794 |

Number of pages | 12 |

Journal | Journal of Chemical Physics |

Volume | 104 |

Issue number | 24 |

Publication status | Published - 1996 Jun 22 |

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### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

_{3}I*→CH

_{3}+I, CH

_{3}+I*, and CD

_{3}I*→CD

_{3}+I, CD

_{3}+I*.

*Journal of Chemical Physics*,

*104*(24), 9783-9794.

**Full nine-dimensional ab initio potential energy surfaces and trajectory studies of A-band photodissociation dynamics : CH _{3}I*→CH_{3}+I, CH_{3}+I*, and CD_{3}I*→CD_{3}+I, CD_{3}+I*.** / Amatatsu, Yoshiaki; Yabushita, Satoshi; Morokuma, Keiji.

Research output: Contribution to journal › Article

_{3}I*→CH

_{3}+I, CH

_{3}+I*, and CD

_{3}I*→CD

_{3}+I, CD

_{3}+I*',

*Journal of Chemical Physics*, vol. 104, no. 24, pp. 9783-9794.

_{3}I*→CH

_{3}+I, CH

_{3}+I*, and CD

_{3}I*→CD

_{3}+I, CD

_{3}+I*. Journal of Chemical Physics. 1996 Jun 22;104(24):9783-9794.

}

TY - JOUR

T1 - Full nine-dimensional ab initio potential energy surfaces and trajectory studies of A-band photodissociation dynamics

T2 - CH3I*→CH3+I, CH3+I*, and CD3I*→CD3+I, CD3+I*

AU - Amatatsu, Yoshiaki

AU - Yabushita, Satoshi

AU - Morokuma, Keiji

PY - 1996/6/22

Y1 - 1996/6/22

N2 - The full nine-dimensional potential energy surfaces (PESs) of the 3Q0 and 1Q1 states of CH3I have been calculated with the ab initio contracted spin-orbit configuration interaction method. The results are fitted to three diabatic potential terms and their couplings as functions of all the internal degrees of freedom. The transition dipole at the Franck-Condon region has also been calculated. Surface hopping quasiclassical trajectory calculations on these potential energy surfaces have been performed to examine the photodissociation dynamics of both CH3I and CD3I in the A-continuum. The results are in general good agreement with the recent experimental findings. The reasonable I*/(I*+I) branching ratio can be obtained with these PESs when the contribution of direct transition to the 1Q1 state is considered. The rotational distribution of the CH3 and CD3 fragments and its I*/(I*+I)-channel selectivity are determined by the shape of the PESs with respect to the bending angle outside the conical intersection region. The vibrational distribution of umbrella mode is closely related to the shape of PESs for the umbrella angle; the sudden switch of reaction coordinate from 3Q0 to 1Q1 at the conical intersection is the origin of vibrational excitation in the I* channel. The larger umbrella excitation of the CD3 fragment in both I and I* channels, in comparison with the CH3 fragment, is related to the larger separation of the reaction coordinate from the Franck-Condon geometry. The symmetric stretching energy increases during the dissociation, which is related to the shape of PESs with respect to this coordinate, and the excitation of symmetric stretching mode seems to be possible.

AB - The full nine-dimensional potential energy surfaces (PESs) of the 3Q0 and 1Q1 states of CH3I have been calculated with the ab initio contracted spin-orbit configuration interaction method. The results are fitted to three diabatic potential terms and their couplings as functions of all the internal degrees of freedom. The transition dipole at the Franck-Condon region has also been calculated. Surface hopping quasiclassical trajectory calculations on these potential energy surfaces have been performed to examine the photodissociation dynamics of both CH3I and CD3I in the A-continuum. The results are in general good agreement with the recent experimental findings. The reasonable I*/(I*+I) branching ratio can be obtained with these PESs when the contribution of direct transition to the 1Q1 state is considered. The rotational distribution of the CH3 and CD3 fragments and its I*/(I*+I)-channel selectivity are determined by the shape of the PESs with respect to the bending angle outside the conical intersection region. The vibrational distribution of umbrella mode is closely related to the shape of PESs for the umbrella angle; the sudden switch of reaction coordinate from 3Q0 to 1Q1 at the conical intersection is the origin of vibrational excitation in the I* channel. The larger umbrella excitation of the CD3 fragment in both I and I* channels, in comparison with the CH3 fragment, is related to the larger separation of the reaction coordinate from the Franck-Condon geometry. The symmetric stretching energy increases during the dissociation, which is related to the shape of PESs with respect to this coordinate, and the excitation of symmetric stretching mode seems to be possible.

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UR - http://www.scopus.com/inward/citedby.url?scp=0001563455&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0001563455

VL - 104

SP - 9783

EP - 9794

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 24

ER -