Françoise Launay

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

High resolution absorption spectrum of CO2 between 10 and 14 eV

The gas-phase absorption spectra of 12CO2 and 13CO2 between 880 and 2000 A, at a resolution limit of 0·008 A, were recently photographed dy Cossart-Magos et al. Rotational structure observed at 1106 A was then assigned to absorption to the … 1π3 g 3pπ u 3Σ- u Rydberg state. The whole region between 898 and 1145 A is now analysed. Ab initio calculations are carried out to estimate the energy of the lower Rydberg states of the s, p, d and f series converging to [Xtilde] 2Π g CO+ 2. nf transition bands are characterized by sharp features in their rotational contours and assigned from n = 4 to n = 28 and 32, respectively for the limits Ωc = 3/2 and 1/2 in the [Xtilde] 2Π g state of the ion core. A new value of the first ionization potential of CO2 results: 111 201 ± 2 cm-1 (average of the two limits). np transition bands, with the exception of the 1106 A band referred to above, are diffuse, and were assigned by a method based on comparison of experimental and calculated quantum defects plotted against the red...

The optical spectrum of the doubly charged molecular nitrogen ion: Rotational analysis of the (0-0) and (1-1) bands of the D1Σu+-X1Σg+ transition of N22+: Comparison of observations with Ab-initio calculation results

Abstract Emission spectra obtained in the 1550–1650 A region with a 10-m vuv spectrograph are conclusively assigned to the N 2 2+ ion. The 1589-A band, previously observed by Carroll, and a new band of the same system, have been rotationally analyzed. Ab-initio calculations have been performed which support the assignment of these two bands to the D 1 Σ u + - X 1 Σ g + system. The calculations also explain the observed breaking-off points in the branch structure as well as weakening and broadening of the other expected bands. These phenomena arise from electron configuration changes and perturbation effects in the ground state.

Effect of rotational coupling on emission probabilities of Lyman and Werner band systems of the vacuum ultraviolet spectrum of H2

Ratios of emission probabilities of rotational lines of the Lyman and Werner band systems, B 1∑+u →X 1∑+g and C 1∏u →X1∑+g, respectively, are calculated by different methods. These theoretical ratios are compared to the experimental intensity ratios of about a hundred lines selected from a vacuum ultraviolet emission spectrum whose intensity is investigated for the first time at high resolution. The computation permits to compare two ways of solving a system of two coupled equations with discrete eigenvalues. In most cases the effect of the mutual rotational perturbation between B and C states is found significant on the ratio of P and R line intensities. Ambiguity in labeling a few B and C levels is discussed.

Modelling the VUV emission spectrum of N2: preliminary results on the effects of rotational interactions on line intensities.

A theoretical model of the excited singlet ungerade electronic states of the nitrogen molecule is presented. This work is an extension of a previous study (D. Stahel, M. Leoni and K. Dressler, J. Chem. Phys. 79, 2541-2558, 1983) with the addition of rotational interactions between states of different symmetry. These rotational interactions together with the homogeneous couplings frequently lead to extreme mixing of the states. This model is being used to analyse the high resolution vacuum ultraviolet emission spectrum which is currently being recorded photoelectrically. The ultimate goal of this work is the reliable interpretation of the low resolution emission spectra observed from planetary atmospheres, notably that of Titan, and the transitions assigned as being important in the Voyager 1 spectra of Titan are discussed in detail.

High resolution absorption spectrum of CO2 between 1750 and 2000 Å

The absorption spectrum of CO2 gas between 1750 and 2000 A has been photographed at high resolution and proves to be extremely rich in bands with considerable rotational fine structure. In spite of the great complexity, we have been able to achieve a coherent preliminary analysis of 9 bands defining an excited state bending progression and which are among the stronger bands in this spectral region. The symmetry species obtained for the upper levels is consistent with their assignment to the 11A2 state, rendered vibronically allowed by excitation of one quantum of the asymmetric stretching v′3(b2) vibration. The assignments are discussed in relation to recent ab initio calculations. Many perturbations are present in the spectra and some of these have been satisfactorily explained.

The vacuum uv emission spectrum of the 15N22+ molecular ion

Abstract The vacuum uv emission of the 15N22+ ion has been recorded for the first time. Rotational analysis of two bands, analogous to those already observed in the case of the natural isotope, confirm their assignment to the D1Σu+-X1Σg+ (0, 0) and (1, 1) bands. More precise data are also obtained for the 3Σg− state which perturbs ground state vibrational levels.

High resolution vacuum ultraviolet emission spectrum of D2 from 78to103nm: The DΠu1→XΣg+1 and D′Πu−1→XΣg+1 band systems

The emission spectrum of the D2 molecule has been studied at high resolution in the vacuum ultraviolet region 78.5–102.7nm. A detailed analysis of the two DΠu1→XΣg+1 and D′Πu−1→XΣg+1 electronic band systems is reported. New and improved values of the level energies of the two upper states have been derived with the help of the program IDEN [V. I. Azarov, Phys. Scr. 44, 528 (1991); 48, 656 (1993)], originally developed for atomic spectral analysis. A detailed comparison is made between the observed energy levels and solutions of coupled equations using the newest ab initio potentials by Wolniewicz and co-workers [J. Chem. Phys. 103, 1792 (1995); 99, 1851 (1993); J. Mol. Spectros. 212, 208 (2002); 220, 45 (2003)] taking into account the nonadiabatic coupling terms for the DΠu1 state with the lowest electronic states BΣu+1, CΠu1, and B′Σu+1. A satisfactory agreement has been found for most of the level energies belonging to the D and D′ states. The remaining differences between observation and theory are pro...

Spectroscopic analysis of the transverse excited C(3)Pi(u) ? B(3)Pi(g) (0-0) uv laser band of N(2) at room temperature.

A new high-resolution spectroscopic study of the 0-0 transition (3371 A) in the N(2) Second Positive System excited by a pulsed transverse electrical discharge has been carried out with a 14-m Czerny-Turner spectrograph. A detailed rotational analysis of the spectrum has pointed out a few misassignments in the earlier work of Dieke and Heath. The simple model proposed by Patel has been applied to the nitrogen laser in order to explain the optical gain formation on the different branches. The experimental results are in reasonable agreement with the theoretical model.

New emission bands in the high resolution vacuum ultra-violet spectrum of molecular nitrogen

Abstract The vacuum ultra-violet (V.U.V.) emission spectrum of N2, produced by a low pressure discharge, is investigated at high resolution from 107.8 nm down to 85 nm. Tens of newly observed bands show up at short wavelength. Cross-examination of emission and absorption spectra reveals that most of apparent intensity anomalies in rotational structures arise from radiation trapping, by accidental coincidence of an emission line with an absorption line from another band. It is concluded that very few anomalies can be ascribed to predissociation.