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Indirect predissociation of the b′ 1Σu+(v = 20) level of N2 is studied experimentally by vacuum-ultraviolet photoabsorption employing synchrotron radiation and a Fourier-transform spectrometer, and interpreted with the aid of a quantitative model of interacting 1Πu and 1Σu+, bound and unbound states which solves the coupled Schrödinger equation. An observed rotationally-localised peak in the b′(20) predissociation linewidths is identified by the model as arising from an interaction with a strongly predissociated and unobserved bound level of the mixed c3 1Πu and o3 1Πu Rydberg states. This leads to the dissociation of b′(20) into the continuum of the b 1Πu valence state. The residual observed predissociation of b′ 1Σu+(v = 20) apart from the rotationally-localised peak cannot be explained by a mechanism of 1Πu and 1Σu+ interaction, and must involve states of higher multiplicity.

We carried out experiments at the SOLEIL synchrotron facility to acquire data for modelling CO photochemistry in the vacuum ultraviolet. We report oscillator strengths and predissociation rates for four vibrational bands associated with transitions from the v = 0 level of the X¹Σ+ ground state to the v = 0-3 vibrational levels of the core excitedW¹Π Rydberg state, and for three overlapping bands associated with the 4pπ, 5pπ, and 5σ Rydberg states between 92.9 and 93.4 nm in 13C18O. These results complete those obtained in the same conditions for 12C16O, 13C16O, and 12C18O recently published by us, and extend the development of a comprehensive database of line positions, oscillator strengths, and linewidths of photodissociating transitions for CO isotopologues. Absorption spectra were recorded using the Vacuum UltraViolet Fourier Transform Spectrometer (VUV-FTS) installed on the Dichroïsme Et Spectroscopie par Interaction avec le Rayonnement Synchrotron (DESIRS) beamline at SOLEIL. The resolving power of the measurements, R = 300 000 to 400 000, allows the analysis of individual line strengths and widths within the bands. Gas column densities in the differentially pumped system were calibrated using the B-X (0-0) band at 115.1 nm in 13C18O. [ABSTRACT FROM AUTHOR]

Models of astronomical environments containing CO require accurate molecular data to reproduce and interpret observations. We conduct experiments at the SOLEIL synchrotron facility to acquire data to model CO photochemistry in the vacuum ultraviolet. The improvement in UV spectroscopic instrumentation in both sensitivity and resolution provides more accurate laboratory spectroscopic determinations. We continue our work on photoabsorption oscillator strengths and predissociation rates for 12C16O; we report new measurements for two additional isotopologues, 13C16O and 12C18O, 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 four overlapping bands (three resolved and one diffuse) between 92.97 and 93.35 nm. Some of the latter include unidentified perturbations. Absorption spectra were recorded using the vacuum-ultraviolet Fourier-transform spectrometer that is installed on the DESIRS beamline at SOLEIL which provides 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+ (v′ = 0,v′′ = 0) band. Absorption bands are analyzed by synthesizing line and band profiles and fitting them to the measured spectra. These considerably improved results are compared with earlier determinations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]