High-resolution study of oscillator strengths and predissociation rates for¹²C¹⁶O

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 12 C 16 O at 295 K and 77 K, of four bands from X 1 Σ + (v = 0) to the v = 0-3 vibrational levels of the core-excited W 1 Π 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 1 Σ + -X 1 Σ + (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.

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

“…Special techniques are required to record ultraviolet photoabsorption spectra for wavelengths shorter than 105 nm due to the lack of transmitting material for use as windows or beam splitters. For example, utilising frequency-multiplied lasers (e.g., Ubachs 2005;Stark et al 1999), synchrotron radiation sources (e.g., Yoshino et al 2006) and, recently, the vacuum-ultraviolet Fourier transform spectrometer at the SOLEIL synchrotron (de Oliveira et al 2011;Eidelsberg et al 2012), or occasionally the interstellar laboratory (e.g., Federman et al 2001). The interpretation of experimental photoabsorption spectra is generally straight-forward except where the instrumental spectral resolution is insufficient to resolve detailed structure of molecules with non-continuum absorption (cf., N 2 as opposed to CH 4 in Sect.…”

VIS and VUV spectroscopy of 12C17O and deperturbation analysis of the A1Π, υ = 1–5 levels

“…The 1s uncertainty due to fitting errors of measured wavenumbers (exclusive of calibration uncertainty) was estimated from the least-squares optimisation algorithm and varies between 0.002 and 0.1 cm À1 for the strongest and weakest lines, respectively. The ratio of the gases used in the experiment was 12 25,[71][72][73] A brief summary of the steps involved in our spectral modelling is as follows:…”

Observation of a new electronic state of CO perturbing $\bm {W\,{}^1\Pi (v=1)}$WΠ1(v=1)

“…[1][2][3][4][5] These phenomena are of relevance to astrophysics because CO is the second most abundant molecule in the Universe (following H 2 ) and chemically stable, and therefore provides a sink of C and O atoms, limiting the formation of larger C-and O-bearing molecules. 6,7 The liberation of CO's constituent atoms is principally achieved by VUV photodissociation in regions exposed to radiation having a wavelength shorter than 120 nm.…”

“…The W 1 state consists of a 3sσ Rydberg electron built on the A 2 excited state of CO + and leads to several prominent bands in the 90-100 nm region of the ground-state absorption spectrum. Recent measurements of the W (v ) − X(0) absorption bands with v = 0 − 4 were performed by Eidelsberg et al 1,4 for the 12 C 16 O, 13 C 16 O, and 12 C 18 O isotopologues, giving rotationally-resolved f-values and linewidths. These detailed measurements revealed large rotational dependences in these quantities for the majority of bands.…”