The dissociation dynamics of He I 35Cl(B,v =2, 3) complexes with varying amounts of internal energy

Joshua P. Darr, Richard A. Loomis, Anne B. McCoy

Research output: Contribution to journalArticle

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Abstract

The He I 35Cl intermolecular vibrational levels with n =0-6 that are bound within the He+ICl(B,v =3) potential [A. B. McCoy, J. P. Darr, D. S. Boucher, P. R. Winter, M. D. Bradke, and R. A. Loomis, J. Chem. Phys. 120, 2677 (2004)] are identified in laser-induced fluorescence experiments performed at very low temperatures within a supersonic expansion. Comparisons of the positions and intensities of these lines with the excitation spectra, calculated using potential surfaces to describe the interactions between the helium atom and ICl in its ground and excited state, assist in the assignments. Based on these comparisons the excited state potential was rescaled so that the experimental and calculated J =0 energies agree to within the experimental uncertainties for all but the lowest, n =0, intermolecular level. Two-laser, action, and pump-probe spectroscopy experiments indicate that the bound He I 35Cl(B,v =3) intermolecular vibrational levels undergo vibrational predissociation forming rotationally excited I 35Cl(B,v =2,j ) products with distributions that depend upon the initial intermolecular vibrational level excited. Action spectra recorded in the ICl B-X, 2-0 region while monitoring the Δv=0, I 35Cl(B,v =2) channel reveal two additional dissociation mechanisms for the He I 35Cl(B,v ) excited state complexes: rotational predissociation of discrete metastable states lying slightly above the He+I 35Cl(B, v =2) asymptote and direct dissociation that occurs when the linear conformer is excited to the continuum of states above the same asymptote. The rotational predissociation pathway forms I 35Cl(B,v =2,j ) products in all of the rotational states energetically accessible. The direct dissociation mechanism yields very cold rotational product state distributions; for instance, the average rotational energy in the product state distribution measured when the linear complexes are prepared 20 cm -1 above the dissociation limit is only 1.51 cm -1, representing only 7.6% of the available energy.

Original languageEnglish (US)
Article number044318
JournalJournal of Chemical Physics
Volume122
Issue number4
DOIs
StatePublished - Aug 8 2005

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internal energy
Excited states
dissociation
asymptotes
products
excitation
Helium
Lasers
rotational states
helium atoms
metastable state
laser induced fluorescence
Ground state
energy
Experiments
Fluorescence
Pumps
Spectroscopy
pumps
continuums

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

The dissociation dynamics of He I 35Cl(B,v =2, 3) complexes with varying amounts of internal energy. / Darr, Joshua P.; Loomis, Richard A.; McCoy, Anne B.

In: Journal of Chemical Physics, Vol. 122, No. 4, 044318, 08.08.2005.

Research output: Contribution to journalArticle

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abstract = "The He I 35Cl intermolecular vibrational levels with n ′=0-6 that are bound within the He+ICl(B,v ′=3) potential [A. B. McCoy, J. P. Darr, D. S. Boucher, P. R. Winter, M. D. Bradke, and R. A. Loomis, J. Chem. Phys. 120, 2677 (2004)] are identified in laser-induced fluorescence experiments performed at very low temperatures within a supersonic expansion. Comparisons of the positions and intensities of these lines with the excitation spectra, calculated using potential surfaces to describe the interactions between the helium atom and ICl in its ground and excited state, assist in the assignments. Based on these comparisons the excited state potential was rescaled so that the experimental and calculated J ′=0 energies agree to within the experimental uncertainties for all but the lowest, n ′=0, intermolecular level. Two-laser, action, and pump-probe spectroscopy experiments indicate that the bound He I 35Cl(B,v ′=3) intermolecular vibrational levels undergo vibrational predissociation forming rotationally excited I 35Cl(B,v ′=2,j ′) products with distributions that depend upon the initial intermolecular vibrational level excited. Action spectra recorded in the ICl B-X, 2-0 region while monitoring the Δv=0, I 35Cl(B,v ′=2) channel reveal two additional dissociation mechanisms for the He I 35Cl(B,v ′) excited state complexes: rotational predissociation of discrete metastable states lying slightly above the He+I 35Cl(B, v ′=2) asymptote and direct dissociation that occurs when the linear conformer is excited to the continuum of states above the same asymptote. The rotational predissociation pathway forms I 35Cl(B,v ′=2,j ′) products in all of the rotational states energetically accessible. The direct dissociation mechanism yields very cold rotational product state distributions; for instance, the average rotational energy in the product state distribution measured when the linear complexes are prepared 20 cm -1 above the dissociation limit is only 1.51 cm -1, representing only 7.6{\%} of the available energy.",
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