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Astron. Astrophys. 347, 375-390 (1999)


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High resolution emission spectroscopy of the A [FORMULA] - X [FORMULA] fourth positive band system of CO excited by electron impact

Luther W. Beegle, Joseph M. Ajello, Geoffrey K. James, Dariusz Dziczek and Marcos Alvarez

Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 183-601 Pasadena, CA 91109, USA

Received 22 October 1998 / Accepted 25 March 1999

Abstract

We report electron-impact-induced medium resolution fluorescence spectra of CO [310 m[FORMULA] and 366 m[FORMULA] full width at half maximum (FWHM)] at 100 eV over the spectral region from 1300 to 2050 [FORMULA]. Features in the far ultraviolet (FUV) emission spectra correspond to the Fourth Positive band system of CO (A [FORMULA] - X [FORMULA]), together with atomic multiplets from C and O and their ions. The absolute electronic transition moment as a function of internuclear distance was determined from relative band intensities scaled to oscillator strength measurements. A model of the vibronic structure of the band system was developed using the laboratory measurement of the electronic transition moment. In addition, we have obtained high resolution spectra ([FORMULA] 34 m[FORMULA] FWHM) of the CO (A-X) (5,1) band at 1435 [FORMULA] and the (3,0) band at 1447 [FORMULA] and accurately modeled the rotational line structure. The excitation function of the (0,1) band at 1597 [FORMULA] was measured in the electron impact energy range from threshold to 750 eV and normalized at 100 eV using the relative flow technique with the standard NI (1200 [FORMULA]) cross section from dissociative excitation of N2. The CO (A-X) band system emission cross section was established from a measurement of the relative band intensities of CO at 100 eV. The total Fourth Positive band system cascade cross section, arising from (B [FORMULA] A) and (C [FORMULA] A) transitions, is [FORMULA] 6% of the emission cross section at 100 eV. The high resolution line profile of the 1152 [FORMULA] atomic O multiplet (1D0- 1D) resulting from dissociative excitation of CO was measured at [FORMULA] 22 m[FORMULA] FWHM. Kinetic energy distributions of the atomic O fragments at 30 eV and 100 eV impact energies were obtained from an analysis of the deconvolved true line profiles.

Key words: molecular data – ISM: molecules – ultraviolet: ISM

Send offprint requests to: Joseph M. Ajello

© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999

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