High-resolution study of oscillator strengths and predissociation rates for ¹²C¹⁶O

W-X bands and Rydberg complexes between 92.9 and 93.4 nm

M. Eidelsberg¹, J. L. Lemaire^1,2, S. R. Federman³, G. Stark⁴, A. N. Heays⁴, Y. Sheffer³, L. Gavilan^1,2, J.-H. Fillion⁵, F. Rostas¹, J. R. Lyons⁶, P. L. Smith⁷, N. de Oliveira⁸, D. Joyeux⁸, M. Roudjane⁸ and L. Nahon⁸

¹ Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France
e-mail: michele.eidelsberg@obspm.fr; francois.rostas@obspm.fr; jean-louis.lemaire@obspm.fr;
² LAMAp/LERMA, Université de Cergy-Pontoise, 95031 Cergy-Pontoise, France
e-mail: jean-louis.lemaire@obspm.fr; lisseth.gavilan@obspm.fr
³ Department of Physics and Astronomy, University of Toledo, Toledo, OH, USA
e-mail: steven.federman@utoledo.edu; ysheffer@astro.umd.edu
⁴ Department of Physics, Wellesley College, Wellesley, MA, USA
e-mail: gstark@wellesley.edu;aheays@yahoo.com
⁵ LPMAA, Université UPMC, Paris 06 and CNRS, UMR 7092, 75006 Paris, France
e-mail: jean-hugues.fillion@upmc.fr
⁶ Department of Earth and Space Sciences, UCLA, Los Angeles, CA, USA
e-mail: jimlyons@ucla.edu
⁷ 93 Pleasant Street, Watertown, MA 02472, USA
e-mail: plsmith44@gmail.com
⁸ DESIRS beam line, Synchrotron SOLEIL, Saint Aubin, France
e-mail: nelson.de.oliveira@synchrotron-soleil.fr

Received: 31 December 2011
Accepted: 13 February 2012

Abstract

Models of astronomical environments containing CO require accurate molecular data to reproduce and interpret observations. We are conducting experiments at the SOLEIL synchrotron facility to acquire data for modeling CO photochemistry in the vacuum ultraviolet. The improvement in UV spectroscopic instrumentation, both in sensitivity and resolution, provides more accurate laboratory spectroscopic determinations. We report new measurements yielding photoabsorption oscillator strengths and predissociation rates, for ¹²C¹⁶O at 295 K and 77 K, of four bands from X ¹Σ⁺ (v′′ = 0) to the v′ = 0–3 vibrational levels of the core-excited W ¹Π Rydberg state and for six overlapping bands between 92.97 and 93.35 nm. Absorption spectra were recorded using the vacuum ultraviolet Fourier transform spectrometer installed on the DESIRS beamline at SOLEIL, providing a resolving power R = 350 000. This resolution allows the analysis of individual line strengths and widths in the electronic transitions and the identification of a previously unobserved perturbation in the W(1) level. Gas column densities in the differentially-pumped system were calibrated using the B ¹Σ⁺ – X ¹Σ⁺(0, 0) band. Absorption bands are analyzed by synthesizing line and band profiles with independently developed codes. These considerably improved results are compared with earlier determinations.