A Laboratory Study of C_3H^+ and the C_3H Radical in Three New Vibrationally Excited ^2Σ States Using a Pin-Hole Nozzle Discharge Source
Abstract
Rotational lines of the positive molecular ion C_3H^+ and of the neutral C_3H radical in three new vibrationally excited states with ^2Σ symmetry have been detected in a supersonic molecular beam in the centimeter-wave band. The fundamental rotational line of the ion is quite weak, but is observed with similar intensity in a dc discharge through several different hydrocarbon gases when helium is the buffer gas. Under these conditions, the fractional abundance of C_3H^+ relative to C_3H is estimated to be of order 10^(−4), i.e., toward the lower end of the ratio (10^(−3)–10^(−4)) found for protonated ions using the same discharge nozzle. For each new ^2Σ state of the C_3H radical, spectroscopic constants, including those describing hydrogen hyperfine structure, have been determined to high precision. Lines of one ^2Σ state (B = 11271 MHz) are particularly intense in our molecular beam; for this state and a second one (B = 11306 MHz), millimeter-wave transitions have also been observed between 180 and 340 GHz using a long path dc glow absorption spectrometer. On the basis of intensity measurements with this spectrometer, the inferred rotation–vibration constant α, and theoretical calculations, the state with B = 11271 MHz is tentatively assigned to the ν_5 bending mode, predicted to lie ~300 cm^(−1) above ground.
Additional Information
© 2015 American Astronomical Society. Received 2014 December 3; accepted 2015 January 28; published 2015 March 12. We thank the anonymous referee for extremely helpful comments regarding how the hydrogen Fermi-contact parameters might be used to support the vibrational assignments, H. Gupta, M. Gerin, S. Thorwirth, and H.S.P. Müller for discussions, and B. Rocher for assistance during initial searches for C_3H^+ in our laboratory. The experimental work is supported by NASA grant NNX13AE59G. K.N.C. was supported by a CfA Postdoctoral Fellowship from the Smithsonian Astrophysical Observatory, and B.A.M. is supported by a Janksy Fellowship from NRAO. We also thank E.S. Palmer and P. Antonucci for technical assistance.Attached Files
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Additional details
- Eprint ID
- 57908
- Resolver ID
- CaltechAUTHORS:20150529-122929513
- NNX13AE59G
- NASA
- Smithsonian Astrophysical Observatory
- National Radio Astronomy Observatory, Jansky Fellowship
- Created
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2015-05-29Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field