Ultraviolet Measurements of Interstellar C2

Abstract

We analyzed archival spectra acquired with the Hubble Space Telescope for a study of interstellar C2. Absorption from the electronic transitions, D ^1Sigma^+_u -- X ^1Sigma^+_g (0,0) as well as F ^1Pi_u -- X ^1Sigma^+_g (0,0) and (1,0), was the focus of the study. Our profile syntheses revealed that the lines of the F-X bands were broadened as a result of a perturbation involving the upper levels. Further evidence for the perturbation came from anomalies in line strength and position for the F-X (0,0) band. The perturbation likely arises from a combination of triplet-singlet interactions involving spin-orbit mixing between ^3Pi_u states and F ^1Pi_u and an avoided crossing between the ^3Pi_u states. Tunneling through a potential barrier caused by the 3 and 4 ^1Pi_u states and spin-orbit mixing with other close-lying triplet states of ungerade symmetry are less likely. Except for the broadening, lines in the F-X (1,0) band appear free from anomalies and can be used to study interstellar C2; new results for 10 sight lines are presented.

17 pages, 3 tables, 3 figures, to appear in ApJ

References in corpus (6)

• Ultraviolet Survey of CO and H_2 in Diffuse Molecular Clouds: The Reflection of Two Photochemistry Regimes in Abundance Relationships
• Abundances and Behavior of 12CO, 13CO, and C2 in Translucent Sight Lines
• Cloud Structure and Physical Conditions in Star-Forming Regions from Optical Observations. II. Analysis
• Hubble Space Telescope Survey of Interstellar ^12CO/^13CO in the Solar Neighborhood
• Abundances and rotational temperatures of the C2 interstellar molecule towards six reddened early-type stars
• Physical Conditions in the Foreground Gas of Reflection Nebulae: NGC 2023, vdB 102, and NGC 7023

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• Multireference configuration interaction study of the predissociation of C${}_2$ via its $F{}^1{\Pi }_u$ state
• First detection of $A$--$X$ (0,0) bands of interstellar C${}_2$ and CN
• The EDIBLES Survey. VII. A survey of C2 and C3 in interstellar clouds
• The Transition from Diffuse Molecular Gas to Molecular Cloud Material in Taurus