### Abstract

Electronic structure methods and nonperturbative resonance theory are applied to study the radiative and radiationless decay mechanisms of the MgBr (A ^{2}Π_{Ω}) vibrational levels. The X ^{2}Σ^{+} and 1,2 ^{2}Π_{Ω} adiabatic electronic states are characterized using ab initio state-averaged multiconfigurational self-consistent field/second order configuration interaction wave functions. Interstate derivative couplings between the ^{2}Π states have been calculated and used to construct a rigorous diabatic basis. The nonrelativistic potential energy curves are modified in the first order of degenerate perturbation theory to take account of the spin-orbit interactions treated within Breit-Pauli approximation. All vibrational levels in the A ^{2}Π_{Ω} manifold are resonances predissociated by the repulsive 2 ^{2}Π state. A recently developed computational approach [S. Han and D. R. Yarkony, Mol. Phys. 88, 53 (1996)] based on a Feshbach formalism is employed to determine energies, linewidths, and radiative and radiationless decay rates in a coupled diabatic states basis within a Hund's case (a) approximation. Large nonadiabatic interactions cause significant energy shifts in the resonances levels. It is shown that a pronounced Ω-dependence in the radiationless decay rates results from the large fine structure splitting in the 2 ^{2}Π_{Ω} diabatic state which corresponds to Mg(^{1}S)Br(^{2}P). Comparisons with absorption and fluorescence spectra reveal important insights into A ^{2}Π_{Ω} state decay. The spectroscopic constants of the A ^{2}Π_{Ω}, Ω=3/2 and 1/2 states and the A ^{2}Π_{3/2} state predissociation are well described in a Hund's case (a) approximation. However it is found that the A ^{2}Π_{1/2} state predissociation is significantly underestimated in this limit. Rather the A ^{2}Π_{1/2} state is indirectly predissociated by the 2 ^{2}Π_{3/2} state through rotational coupling to the A ^{2}Π_{3/2} state.

Original language | English (US) |
---|---|

Pages (from-to) | 4091-4101 |

Number of pages | 11 |

Journal | Journal of Chemical Physics |

Volume | 106 |

Issue number | 10 |

State | Published - Mar 8 1997 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics

### Cite this

^{2}Π

_{Ω}state of MgBr.

*Journal of Chemical Physics*,

*106*(10), 4091-4101.

**Resonances in the predissociation of the A ^{2}Π_{Ω} state of MgBr.** / Sadygov, Rovshan; Rostas, Joëlle; Taieb, Guy; Yarkony, David R.

Research output: Contribution to journal › Article

^{2}Π

_{Ω}state of MgBr',

*Journal of Chemical Physics*, vol. 106, no. 10, pp. 4091-4101.

^{2}Π

_{Ω}state of MgBr. Journal of Chemical Physics. 1997 Mar 8;106(10):4091-4101.

}

TY - JOUR

T1 - Resonances in the predissociation of the A 2ΠΩ state of MgBr

AU - Sadygov, Rovshan

AU - Rostas, Joëlle

AU - Taieb, Guy

AU - Yarkony, David R.

PY - 1997/3/8

Y1 - 1997/3/8

N2 - Electronic structure methods and nonperturbative resonance theory are applied to study the radiative and radiationless decay mechanisms of the MgBr (A 2ΠΩ) vibrational levels. The X 2Σ+ and 1,2 2ΠΩ adiabatic electronic states are characterized using ab initio state-averaged multiconfigurational self-consistent field/second order configuration interaction wave functions. Interstate derivative couplings between the 2Π states have been calculated and used to construct a rigorous diabatic basis. The nonrelativistic potential energy curves are modified in the first order of degenerate perturbation theory to take account of the spin-orbit interactions treated within Breit-Pauli approximation. All vibrational levels in the A 2ΠΩ manifold are resonances predissociated by the repulsive 2 2Π state. A recently developed computational approach [S. Han and D. R. Yarkony, Mol. Phys. 88, 53 (1996)] based on a Feshbach formalism is employed to determine energies, linewidths, and radiative and radiationless decay rates in a coupled diabatic states basis within a Hund's case (a) approximation. Large nonadiabatic interactions cause significant energy shifts in the resonances levels. It is shown that a pronounced Ω-dependence in the radiationless decay rates results from the large fine structure splitting in the 2 2ΠΩ diabatic state which corresponds to Mg(1S)Br(2P). Comparisons with absorption and fluorescence spectra reveal important insights into A 2ΠΩ state decay. The spectroscopic constants of the A 2ΠΩ, Ω=3/2 and 1/2 states and the A 2Π3/2 state predissociation are well described in a Hund's case (a) approximation. However it is found that the A 2Π1/2 state predissociation is significantly underestimated in this limit. Rather the A 2Π1/2 state is indirectly predissociated by the 2 2Π3/2 state through rotational coupling to the A 2Π3/2 state.

AB - Electronic structure methods and nonperturbative resonance theory are applied to study the radiative and radiationless decay mechanisms of the MgBr (A 2ΠΩ) vibrational levels. The X 2Σ+ and 1,2 2ΠΩ adiabatic electronic states are characterized using ab initio state-averaged multiconfigurational self-consistent field/second order configuration interaction wave functions. Interstate derivative couplings between the 2Π states have been calculated and used to construct a rigorous diabatic basis. The nonrelativistic potential energy curves are modified in the first order of degenerate perturbation theory to take account of the spin-orbit interactions treated within Breit-Pauli approximation. All vibrational levels in the A 2ΠΩ manifold are resonances predissociated by the repulsive 2 2Π state. A recently developed computational approach [S. Han and D. R. Yarkony, Mol. Phys. 88, 53 (1996)] based on a Feshbach formalism is employed to determine energies, linewidths, and radiative and radiationless decay rates in a coupled diabatic states basis within a Hund's case (a) approximation. Large nonadiabatic interactions cause significant energy shifts in the resonances levels. It is shown that a pronounced Ω-dependence in the radiationless decay rates results from the large fine structure splitting in the 2 2ΠΩ diabatic state which corresponds to Mg(1S)Br(2P). Comparisons with absorption and fluorescence spectra reveal important insights into A 2ΠΩ state decay. The spectroscopic constants of the A 2ΠΩ, Ω=3/2 and 1/2 states and the A 2Π3/2 state predissociation are well described in a Hund's case (a) approximation. However it is found that the A 2Π1/2 state predissociation is significantly underestimated in this limit. Rather the A 2Π1/2 state is indirectly predissociated by the 2 2Π3/2 state through rotational coupling to the A 2Π3/2 state.

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M3 - Article

VL - 106

SP - 4091

EP - 4101

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 10

ER -