M. Eidelsberg

Photoabsorption and photodissociation cross sections of CO between 88.5 and 115 nm

Abstract Cross sections for photoabsorption and photodissociation of CO between 88.5 and 115 nm have been measured at a spectral resolution of 0.015 nm using a synchrotron radiation source. Most of the photodissociation is found to occur in rotationally resolved bands and not in continua. The region below 100 nm predominates in the photodissociation rate. The band absorption cross sections of the first Rydberg states are considerably increased with respect to previous studies following a better appreciation of pressure saturation effects. The integrated photodissociation cross section above 91.2 nm, which is of interest in many astrophysical situations, is measured to be 300 ± 40 × 10 −18 cm 2 nm, sharply increased with respect to usually accepted values.

Reinvestigation of the vacuum ultraviolet spectrum of CO and isotopic species: The B1Σ+↔X1Σ+ transition

Abstract The vacuum ultraviolet band spectrum system B1Σ+-X1Σ+ of 12C16O, 13C16O, 12C18O, and 13C18O has been extensively investigated both in absorption and in emission with the Meudon Observatory national 10-m vacuum spectrograph. A band lying at 109.9 nm in 12C16O is observed for all isotopes but only in absorption. It is shown to be the B-X(2-0) band. Molecular parameters of the B(v = 0, 1, 2) levels have been derived from simultaneous least-squares fits of the absorption and emission data pertaining to each of these vibrational levels. In addition, a simultaneous fit of the data for the different isotopes provided mass independent Dunham coefficients and equilibrium constants for the B state. Our values obtained for ωe and ωexe confirm the recent determinations which are in disagreement with the values tabulated in standard references. The emission bands exhibit sudden weakenings typical of predissociation. This predissociation further manifests itself in the v = 2 level by a conspicuous broadening of the absorption lines. It may also be the cause of the displacement and anomalous B values observed for this level. From the Dunham coefficients, the following molecular constants (in cm−1 except for re) for the B state have been derived: T e =86926.9 r 3 =1.1197 A . ω e ω e x e B e α e 10 6 D e 12C16O 2161.75 39.84 1.9613 0.0262 6.5 13C16O 2113.56 38.08 1.8749 0.0245 6.0 12C18O 2109.53 37.93 1.8677 0.0244 5.9 13C18O 2060.12 36.18 1.7812 0.0227 5.4 14C16O 2071.52 36.58 1.8010 0.0231 5.5

Vibrational band oscillator strengths and dipole transition moment of the A 1Π–X 1Σ+ system of CO

Rotationally integrated vibrational absorption cross sections of the A 1Π−X 1Σ+ (v’−0) bands of CO have been measured in the wavelength range 125–155 nm using monochromatized synchrotron radiation as background light source. Absorption cross sections for a few singlet‐triplet transitions are also obtained. Vibrational band oscillator strengths are determined for 0≤v’≤12 and compared to other experimental and theoretical values. It is found that the new data are well reproduced by extrapolating to shorter internuclear distances the parabolic dipole transition moment function determined by De Leon [J. Chem. Phys. 89, 20 (1988); 91, 5859 (1989)]. Deperturbed lifetimes for levels 0≤v’≤13 are calculated from the parabolic dipole moment function and, except for v’=13, are found in good agreement with available experimental results.

Oscillator strengths for transitions to Rydberg levels in 12 C 16 O, 13 C 16 Oa nd 13 C 18 O between 967 and 972 Å

Absorption oscillator strengths have been determined from high-resolution spectra in the 967-972 A region of three CO isotopomers for transitions to the Rydberg levels 4pπ(0), 3dπ(1) and 4pσ(0), as well as to the mixed E(6) level recently characterized by Eidelsberg et al. (2004). Synchrotron radiation from the Super-ACO electron storage ring at Orsay (LURE) was used as a light source. Oscillator strengths were extracted from the recorded spectra by least-squares fitting of the experimental profiles with synthetic spectra taking into account the homogeneous and heterogeneous interactions of the four levels. Column densities were derived from fits to the 3pπ(0) absorption band whose oscillator strength is well established. These are the first reported measurements for 13 C 18 O. For 12 C 16 O, our results are consistent with the larger values obtained in the most recent laboratory and astronomical studies.

Band oscillator strengths of the intersystem transitions of CO

Absorption oscillator strengths of 18 intersystem bands of CO between 1360 and 1620 A originating from the ground state and involving the a′ 3Σ+, e 3Σ−, and d 3Δ states have been measured using synchrotron radiation as a background source. They have also been calculated using the published molecular parameters provided by the standard spectroscopic perturbation analysis, including the spin-orbit interaction with the nearby A 1Π state. It was found, however, that the model used in that analysis had to be extended in order to take into account the contributions of several vibrational levels of the A state to the intensity of a given singlet–triplet band. The present measurements are in good agreement with the predictions of this extended model. The puzzling discrepancies reported earlier between oscillator strength or rotationally resolved lifetime measurements and standard calculations are now well understood as well as the temperature variation of some of these band-integrated oscillator strengths. Line a...

Rotationally resolved rydberg absorption of CO2 at 1106 Å. Assignment and analysis of the π3g3pπu3Σ–uâ†X1Σ+g Transition

The gas-phase absorption spectra of 12CO2 and 13CO2 have been photographed between 880 and 2000 A at a resolution of 0.008 A. The diffuse character of most of the bands in this region was confirmed, but the considerable increase in resolution (× 25) over previous work has enabled us to observe some rotationally resolved bands. Our results show that some previous band assignments in the vacuum ultraviolet spectra of CO2 must be revised. Analysis of the 1106 A band of both isotopic species provides molecular constants for its upper electronic state, which is shown to be linear. The 1106 A band is assigned as the origin of the Rydberg forbidden transition ⋯π3g33pπu3Σ–uâ†�X1Σ+g of CO2. The v2 bending vibration of the 3Σ–u state is found to have a value of 498 cm–1 in 12CO2(483 cm–1 in 13CO2) from assignment of the 211 transition. Our results are used to interpret some aspects of the excitation spectrum and yield of CO2 photodissociation.

High-resolution study of oscillator strengths and predissociation rates for 13C18O - W-X bands and Rydberg complexes between 92.9 and 93.5 nm

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 X1 Σ+ ground state to the v = 0–3 vibrational levels of the core excited W1Π Rydberg state, and for three overlapping bands associated with the 4pπ, 5pπ, and 5pσ 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 Dichroisme 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.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.

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

High-accuracy dispersive optical spectroscopy measurements in the visible (VIS) region have been performed on the less-abundant 12C17O isotopologue, observing high-resolution emission bands of the B1Σ+ (υ = 0) → A1Π (υ = 3, 4, and 5) Angstrom system. These are combined with high-resolution photoabsorption measurements of the 12C17O B1Σ+ (υ = 0) ← X1Σ+ (υ = 0) and C1Σ+ (υ = 0) ← X1Σ+ (υ = 0) Hopfield–Birge bands recorded with the vacuum-ultraviolet (VUV) Fourier transform spectrometer, installed on the DESIRS beamline at the SOLEIL synchrotron. The frequencies of 429 observed transitions have been determined in the 15 100–18 400 cm−1 and 86 900–92 100 cm−1 regions with an absolute accuracy of up to 0.003 cm−1 and 0.005 cm−1 for the B–A, and B–X, C–X systems, respectively. These new experimental data were combined with data from the previously analysed C → A and B → A systems. The comprehensive data set, 982 spectral lines belonging to 12 bands, was included in a deperturbation analysis of the A1Π, υ = 1–5 levels of 12C17O, taking into account interactions with levels in the d3Δi, e3Σ−, a′3Σ+, I1Σ− and D1Δ states. The A1Π and perturber states were described in terms of a set of deperturbed molecular constants, spin–orbit and L-uncoupling interaction parameters, equilibrium constants, 309 term values, as well as isotopologue-independent spin–orbit and rotation-electronic perturbation parameters.

High-resolution spectroscopy of the bands in 13C18O: term values, ro-vibrational oscillator strengths and Hönl–London corrections

Our knowledge of astronomical environments containing CO depends on accurate molecular data to reproduce and interpret observations. The constant improvement in UV space instrumentation, both in sensitivity and resolution, requires increasingly detailed laboratory data. Following a long-term experimental campaign at the SOLEIL Synchrotron facility, we have acquired complete datasets on the CO isotopologues in the vacuum ultraviolet. Absorption spectra were recorded using the Fourier-transform spectrometer installed on the DESIRS beamline, providing a resolving power R > 106 in the 8–12 eV range. Such resolution allows the analysis of individual line positions and strengths in electronic transitions and the location of perturbations. We continue our previous work on A–X bands of 12C16O and 13C16O, reporting here measurements for the 13C18O isotopologue.

High-resolution spectroscopy of the

Our knowledge of astronomical environments containing CO depends on accurate molecular data to reproduce and interpret observations. The constant improvement in UV space instrumentation, both in sensitivity and resolution, requires increasingly detailed laboratory data. Following a long-term experimental campaign at the SOLEIL Synchrotron facility, we have acquired complete datasets on the CO isotopologues in the vacuum ultraviolet. Absorption spectra were recorded using the Fourier-transform spectrometer installed on the DESIRS beamline, providing a resolving power R > 106 in the 8–12 eV range. Such resolution allows the analysis of individual line positions and strengths in electronic transitions and the location of perturbations. We continue our previous work on A–X bands of 12C16O and 13C16O, reporting here measurements for the 13C18O isotopologue.