Intracavity laser photoelectron spectroscopy of Cr2-, Cr2H-, and Cr2D-

Sean M. Casey, Doreen G Leopold

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The photoelectron spectrum of Cr2- shows vibrational levels in the 1Σg+ ground state of the neutral molecule up to 7300 cm-1 above its zero point level. These data, obtained at an instrumental resolution of 5 meV (40 cm-1), reveal a panoramic view of the controversial ground state potential curve of Cr2. Low-lying vibrational levels are found to fit a Morse potential with approximately egae = 479 ± 2 cm-1 and approximately egaeχe = 13.5 ± 1.0 cm-1. This unusually large anharmonicity extrapolates to a dissociation asymptote of only 0.5 eV, considerably lower than the true 1.44 eV value. Between 4875 and 7320 cm-1 above the zero point level, we observe twenty peaks at 130 ± 15 cm-1 intervals, which we assign as transitions from the ground electronic and vibrational state of the anion to high vibrational levels of the Cr2 ground state. Using an RKR inversion procedure, we have obtained a potential curve that fits all of the observed vibrational levels to within our experimental uncertainty. This potential curve is compared with the predictions of Goodgame and Goddard's modified GVB calculation. Transitions to highly excited vibrational levels of the Cr2 ground state are far more intense than would be expected for a direct photodetachment process, and are also strongly wavelength dependent. These non-Franck-Condon intensities are attributed to a resonance of the laser with one or more metastable states of the negative ion far above the electron detachment threshold. The electron affinity of Cr2 is measured to be 0.505 ± 0.005 eV. An excited electronic state of Cr2 with a vibrational frequency of 580 ± 20 cm-1 is observed 14,240 ± 30 cm-1 above the ground state. For Cr2-, we obtain approximately egae = 470 ± 25 cm-1, approximately ega eχe = 20 ± 10 cm-1, and re = 1.71 ± 0.01 angstrom. Tentative state assignments of 1Σu+ or 3Σ u+ for the excited Cr2 state, and 2Σu+ for the anion, are discussed. Preliminary results for Cr2H- and Cr2D- are also presented. The photoelectron spectra of these anions reveal the Cr-Cr and Cr-H stretching frequencies in the neutral molecules, and exhibit partially resolved rotational structure.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
PublisherPubl by Int Soc for Optical Engineering
Pages234-244
Number of pages11
ISBN (Print)0819407844
StatePublished - Jan 1 1992
EventOptical Methods for Time- and State-Resolved Chemistry - Los Angeles, CA, USA
Duration: Jan 23 1992Jan 25 1992

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume1638
ISSN (Print)0277-786X

Other

OtherOptical Methods for Time- and State-Resolved Chemistry
CityLos Angeles, CA, USA
Period1/23/921/25/92

Fingerprint

Laser spectroscopy
Photoelectron spectroscopy
laser spectroscopy
Ground state
photoelectron spectroscopy
Negative ions
ground state
Photoelectrons
State assignment
anions
Morse potential
Electron affinity
Molecules
photoelectrons
curves
Electronic states
Vibrational spectra
Excited states
Stretching
asymptotes

Cite this

Casey, S. M., & Leopold, D. G. (1992). Intracavity laser photoelectron spectroscopy of Cr2-, Cr2H-, and Cr2D-. In Proceedings of SPIE - The International Society for Optical Engineering (pp. 234-244). (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 1638). Publ by Int Soc for Optical Engineering.

Intracavity laser photoelectron spectroscopy of Cr2-, Cr2H-, and Cr2D-. / Casey, Sean M.; Leopold, Doreen G.

Proceedings of SPIE - The International Society for Optical Engineering. Publ by Int Soc for Optical Engineering, 1992. p. 234-244 (Proceedings of SPIE - The International Society for Optical Engineering; Vol. 1638).

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Casey, SM & Leopold, DG 1992, Intracavity laser photoelectron spectroscopy of Cr2-, Cr2H-, and Cr2D-. in Proceedings of SPIE - The International Society for Optical Engineering. Proceedings of SPIE - The International Society for Optical Engineering, vol. 1638, Publ by Int Soc for Optical Engineering, pp. 234-244, Optical Methods for Time- and State-Resolved Chemistry, Los Angeles, CA, USA, 1/23/92.
Casey SM, Leopold DG. Intracavity laser photoelectron spectroscopy of Cr2-, Cr2H-, and Cr2D-. In Proceedings of SPIE - The International Society for Optical Engineering. Publ by Int Soc for Optical Engineering. 1992. p. 234-244. (Proceedings of SPIE - The International Society for Optical Engineering).
Casey, Sean M. ; Leopold, Doreen G. / Intracavity laser photoelectron spectroscopy of Cr2-, Cr2H-, and Cr2D-. Proceedings of SPIE - The International Society for Optical Engineering. Publ by Int Soc for Optical Engineering, 1992. pp. 234-244 (Proceedings of SPIE - The International Society for Optical Engineering).
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N2 - The photoelectron spectrum of Cr2- shows vibrational levels in the 1Σg+ ground state of the neutral molecule up to 7300 cm-1 above its zero point level. These data, obtained at an instrumental resolution of 5 meV (40 cm-1), reveal a panoramic view of the controversial ground state potential curve of Cr2. Low-lying vibrational levels are found to fit a Morse potential with approximately egae = 479 ± 2 cm-1 and approximately egaeχe = 13.5 ± 1.0 cm-1. This unusually large anharmonicity extrapolates to a dissociation asymptote of only 0.5 eV, considerably lower than the true 1.44 eV value. Between 4875 and 7320 cm-1 above the zero point level, we observe twenty peaks at 130 ± 15 cm-1 intervals, which we assign as transitions from the ground electronic and vibrational state of the anion to high vibrational levels of the Cr2 ground state. Using an RKR inversion procedure, we have obtained a potential curve that fits all of the observed vibrational levels to within our experimental uncertainty. This potential curve is compared with the predictions of Goodgame and Goddard's modified GVB calculation. Transitions to highly excited vibrational levels of the Cr2 ground state are far more intense than would be expected for a direct photodetachment process, and are also strongly wavelength dependent. These non-Franck-Condon intensities are attributed to a resonance of the laser with one or more metastable states of the negative ion far above the electron detachment threshold. The electron affinity of Cr2 is measured to be 0.505 ± 0.005 eV. An excited electronic state of Cr2 with a vibrational frequency of 580 ± 20 cm-1 is observed 14,240 ± 30 cm-1 above the ground state. For Cr2-, we obtain approximately egae = 470 ± 25 cm-1, approximately ega eχe = 20 ± 10 cm-1, and re = 1.71 ± 0.01 angstrom. Tentative state assignments of 1Σu+ or 3Σ u+ for the excited Cr2 state, and 2Σu+ for the anion, are discussed. Preliminary results for Cr2H- and Cr2D- are also presented. The photoelectron spectra of these anions reveal the Cr-Cr and Cr-H stretching frequencies in the neutral molecules, and exhibit partially resolved rotational structure.

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