Experimental and theoretical exploration of photodissociation of SO2 via the C1B2 state: Identification of the dissociation pathway

Hideki Katagiri, Tokuei Sako, Akiyoshi Hishikawa, Takeki Yazaki, Ken Onda, Kaoru Yamanouchi, Kouichi Yoshino

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Abstract

The photodissociation reaction of SO2 via the C1B2 state, SO2 (C1B2) → SO(3Σ(~)) + O(3P) was investigated by experimental and theoretical approaches cooperatively to clarify its dissociation mechanism. We measured the laser induced fluorescence (LIF) spectrum of the C-X band in the short UV wavelength region (210-200 nm) under jet-cooled conditions. The fluorescence quantum yields and the dissociation rates of individual vibronic levels were determined in the 220-200-nm region using (i) the LIF spectrum measured in the present study, (ii) that measured previously by Yamanouchi et al. (J. Mol. Struct. 352/353 (1995) 541) in the longer wavelength region above 210 nm, and (iii) the high-resolution absorption spectrum measured by Freeman et al. (Planet. Space. Sci. 32 (1984) 1125). The dissociation rates were also derived in the 210-200-nm region from the broadening of the rotational lines of the C-X vibronic transitions. It was found that the dissociation rates determined through two different procedures were consistent with each other, and that the rate increases almost exponentially as an excess energy above the dissociation threshold increases though there is a certain fluctuation of the dissociation rates reflecting a mode specificity. We also performed theoretical ab initio calculations to derive potential energy surfaces (PESs) of the electronic ground states and low-lying electronically excited states of SO2 within the MCSCF and MRCI levels. The theoretical calculations showed that (i) the PES of the 21A' state (the C1B2 state in C(2v) symmetry), correlating with the SO(1Δ) + O(1D) asymptote, crosses with the repulsive singlet (31A') state, correlating with the SO(3Σ-) + O(3P) asymptote, to form a pseudo-seam, (ii) the crossing pseudo-seam of these two PESs is located near the equilibrium bent angles for the X and C states along the energy contour of ~9700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit, and (iii) the crossing seam between the 21A' (C1B2) and repulsive 23A' states is located in a lower energy region than the singlet seam; at ~6700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit. On the basis of the above experimental and theoretical results together with the previous experimental evidence, we propose that (i) the photodissociation reaction via the C state proceeds mainly through the vibronic mixing between the C state vibronic levels with the quasi-bound dissociation continuum of the electronic ground X1A1 state, and (ii) the additional dissociation channels may be open through the crossing seam with the repulsive singlet (31A') state and that with the repulsive triplet (23A') state in their narrow crossing energy regions.

Original languageEnglish
Pages (from-to)589-614
Number of pages26
JournalJournal of Molecular Structure
Volume413-414
DOIs
Publication statusPublished - Sep 30 1997

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Photodissociation
Potential energy surfaces
Fluorescence
Ground state
Wavelength
Lasers
Quantum yield
Planets
Excited states
Absorption spectra

All Science Journal Classification (ASJC) codes

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry
  • Inorganic Chemistry

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Experimental and theoretical exploration of photodissociation of SO2 via the C1B2 state : Identification of the dissociation pathway. / Katagiri, Hideki; Sako, Tokuei; Hishikawa, Akiyoshi; Yazaki, Takeki; Onda, Ken; Yamanouchi, Kaoru; Yoshino, Kouichi.

In: Journal of Molecular Structure, Vol. 413-414, 30.09.1997, p. 589-614.

Research output: Contribution to journalArticle

Katagiri, Hideki ; Sako, Tokuei ; Hishikawa, Akiyoshi ; Yazaki, Takeki ; Onda, Ken ; Yamanouchi, Kaoru ; Yoshino, Kouichi. / Experimental and theoretical exploration of photodissociation of SO2 via the C1B2 state : Identification of the dissociation pathway. In: Journal of Molecular Structure. 1997 ; Vol. 413-414. pp. 589-614.
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abstract = "The photodissociation reaction of SO2 via the C1B2 state, SO2 (C1B2) → SO(3Σ(~)) + O(3P) was investigated by experimental and theoretical approaches cooperatively to clarify its dissociation mechanism. We measured the laser induced fluorescence (LIF) spectrum of the C-X band in the short UV wavelength region (210-200 nm) under jet-cooled conditions. The fluorescence quantum yields and the dissociation rates of individual vibronic levels were determined in the 220-200-nm region using (i) the LIF spectrum measured in the present study, (ii) that measured previously by Yamanouchi et al. (J. Mol. Struct. 352/353 (1995) 541) in the longer wavelength region above 210 nm, and (iii) the high-resolution absorption spectrum measured by Freeman et al. (Planet. Space. Sci. 32 (1984) 1125). The dissociation rates were also derived in the 210-200-nm region from the broadening of the rotational lines of the C-X vibronic transitions. It was found that the dissociation rates determined through two different procedures were consistent with each other, and that the rate increases almost exponentially as an excess energy above the dissociation threshold increases though there is a certain fluctuation of the dissociation rates reflecting a mode specificity. We also performed theoretical ab initio calculations to derive potential energy surfaces (PESs) of the electronic ground states and low-lying electronically excited states of SO2 within the MCSCF and MRCI levels. The theoretical calculations showed that (i) the PES of the 21A' state (the C1B2 state in C(2v) symmetry), correlating with the SO(1Δ) + O(1D) asymptote, crosses with the repulsive singlet (31A') state, correlating with the SO(3Σ-) + O(3P) asymptote, to form a pseudo-seam, (ii) the crossing pseudo-seam of these two PESs is located near the equilibrium bent angles for the X and C states along the energy contour of ~9700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit, and (iii) the crossing seam between the 21A' (C1B2) and repulsive 23A' states is located in a lower energy region than the singlet seam; at ~6700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit. On the basis of the above experimental and theoretical results together with the previous experimental evidence, we propose that (i) the photodissociation reaction via the C state proceeds mainly through the vibronic mixing between the C state vibronic levels with the quasi-bound dissociation continuum of the electronic ground X1A1 state, and (ii) the additional dissociation channels may be open through the crossing seam with the repulsive singlet (31A') state and that with the repulsive triplet (23A') state in their narrow crossing energy regions.",
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T1 - Experimental and theoretical exploration of photodissociation of SO2 via the C1B2 state

T2 - Identification of the dissociation pathway

AU - Katagiri, Hideki

AU - Sako, Tokuei

AU - Hishikawa, Akiyoshi

AU - Yazaki, Takeki

AU - Onda, Ken

AU - Yamanouchi, Kaoru

AU - Yoshino, Kouichi

PY - 1997/9/30

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N2 - The photodissociation reaction of SO2 via the C1B2 state, SO2 (C1B2) → SO(3Σ(~)) + O(3P) was investigated by experimental and theoretical approaches cooperatively to clarify its dissociation mechanism. We measured the laser induced fluorescence (LIF) spectrum of the C-X band in the short UV wavelength region (210-200 nm) under jet-cooled conditions. The fluorescence quantum yields and the dissociation rates of individual vibronic levels were determined in the 220-200-nm region using (i) the LIF spectrum measured in the present study, (ii) that measured previously by Yamanouchi et al. (J. Mol. Struct. 352/353 (1995) 541) in the longer wavelength region above 210 nm, and (iii) the high-resolution absorption spectrum measured by Freeman et al. (Planet. Space. Sci. 32 (1984) 1125). The dissociation rates were also derived in the 210-200-nm region from the broadening of the rotational lines of the C-X vibronic transitions. It was found that the dissociation rates determined through two different procedures were consistent with each other, and that the rate increases almost exponentially as an excess energy above the dissociation threshold increases though there is a certain fluctuation of the dissociation rates reflecting a mode specificity. We also performed theoretical ab initio calculations to derive potential energy surfaces (PESs) of the electronic ground states and low-lying electronically excited states of SO2 within the MCSCF and MRCI levels. The theoretical calculations showed that (i) the PES of the 21A' state (the C1B2 state in C(2v) symmetry), correlating with the SO(1Δ) + O(1D) asymptote, crosses with the repulsive singlet (31A') state, correlating with the SO(3Σ-) + O(3P) asymptote, to form a pseudo-seam, (ii) the crossing pseudo-seam of these two PESs is located near the equilibrium bent angles for the X and C states along the energy contour of ~9700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit, and (iii) the crossing seam between the 21A' (C1B2) and repulsive 23A' states is located in a lower energy region than the singlet seam; at ~6700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit. On the basis of the above experimental and theoretical results together with the previous experimental evidence, we propose that (i) the photodissociation reaction via the C state proceeds mainly through the vibronic mixing between the C state vibronic levels with the quasi-bound dissociation continuum of the electronic ground X1A1 state, and (ii) the additional dissociation channels may be open through the crossing seam with the repulsive singlet (31A') state and that with the repulsive triplet (23A') state in their narrow crossing energy regions.

AB - The photodissociation reaction of SO2 via the C1B2 state, SO2 (C1B2) → SO(3Σ(~)) + O(3P) was investigated by experimental and theoretical approaches cooperatively to clarify its dissociation mechanism. We measured the laser induced fluorescence (LIF) spectrum of the C-X band in the short UV wavelength region (210-200 nm) under jet-cooled conditions. The fluorescence quantum yields and the dissociation rates of individual vibronic levels were determined in the 220-200-nm region using (i) the LIF spectrum measured in the present study, (ii) that measured previously by Yamanouchi et al. (J. Mol. Struct. 352/353 (1995) 541) in the longer wavelength region above 210 nm, and (iii) the high-resolution absorption spectrum measured by Freeman et al. (Planet. Space. Sci. 32 (1984) 1125). The dissociation rates were also derived in the 210-200-nm region from the broadening of the rotational lines of the C-X vibronic transitions. It was found that the dissociation rates determined through two different procedures were consistent with each other, and that the rate increases almost exponentially as an excess energy above the dissociation threshold increases though there is a certain fluctuation of the dissociation rates reflecting a mode specificity. We also performed theoretical ab initio calculations to derive potential energy surfaces (PESs) of the electronic ground states and low-lying electronically excited states of SO2 within the MCSCF and MRCI levels. The theoretical calculations showed that (i) the PES of the 21A' state (the C1B2 state in C(2v) symmetry), correlating with the SO(1Δ) + O(1D) asymptote, crosses with the repulsive singlet (31A') state, correlating with the SO(3Σ-) + O(3P) asymptote, to form a pseudo-seam, (ii) the crossing pseudo-seam of these two PESs is located near the equilibrium bent angles for the X and C states along the energy contour of ~9700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit, and (iii) the crossing seam between the 21A' (C1B2) and repulsive 23A' states is located in a lower energy region than the singlet seam; at ~6700 cm-1 measured from the SO(3Σ-) + O(3P) dissociation limit. On the basis of the above experimental and theoretical results together with the previous experimental evidence, we propose that (i) the photodissociation reaction via the C state proceeds mainly through the vibronic mixing between the C state vibronic levels with the quasi-bound dissociation continuum of the electronic ground X1A1 state, and (ii) the additional dissociation channels may be open through the crossing seam with the repulsive singlet (31A') state and that with the repulsive triplet (23A') state in their narrow crossing energy regions.

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