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Spectral line positions and emission probabilities of the B′ 1Σu+ → X 1Σg+ and D 1Πu → X 1Σg+ band systems of molecular hydrogen have been calculated by solving a system of four coupled Schrödinger equations. A great number of rotational lines, emitted by a low-pressure electric discharge in H2, have been identified from 122 nm down to 78 nm. All the 69 bands of the B′ 1Σu+ → X 1Σg+ system and many high-J lines of 145 bands of the D 1Πu → X 1Σg+ system are reported for the first time. Improved molecular constants are derived for the (unperturbed) electronic excited state D 1Πu−.

The C 1 Σ + → B 1 Σ + ( v ′ = 0, v ″ = 0) band spectra of the four isotopes of carbon monoxide, 12 C 16 O, 13 C 16 O, 12 C 18 O, and 13 C 18 O have been recorded using a Fourier transform interferometer. The band origins of C - B (0-0) and the rotational constants B 0 and D 0 of the C (0) electronic excited state for the four isotopomers are derived.

Line positions and emission probabilities of the Lyman and Werner band systems of molecular hydrogen have been calculated by solving a system of four coupled Schrodinger equations. We have been able to identify several thousand new lines emitted by a low pressure discharge in H2 from 172 nm down to 78 nm. Many high-J energy levels are reported for the first time. Molecular constants are derived for the (unperturbed) 1Π−u states. Several examples demonstrate that the emission spectrum is very significantly different from that which could be deduced from a knowledge of only the absorption spectrum.

The vacuum ultraviolet emission spectrum of molecular nitrogen, produced by a low pressure discharge, is investigated at high spectral resolution from 107.7 to 124.2nm. Band origins are reported for the 103 bands rotationally analyzed.

The absorption spectrum of the pink afterglow of molecular nitrogen in the vacuum ultraviolet has been analyzed at high resolution. The spectrum exhibits hot bands involving vibrational levels of the electronic ground state as high as v" = 19. Experimentally determined term values are derived for v" = 0-19, of which v" = 16-19 were before now poorly known. Copyright 1999 Academic Press.

The high-resolution emission spectrum of molecular nitrogen was photographed in the vacuum ultraviolet from 82.6 to 124.2 nm. The use of a low-pressure Penning-type electric discharge source has led to considerably reduced self-absorption at short wavelengths, making it possible to record as many as 283 emission bands. All emission bands have been rotationally analyzed, 215 being observed for the first time, and are reported in a separate publication. Energy values were deduced for the nonpredissociative or only slightly predissociative rovibronic levels in 10 singlet electronic excited states. Copyright 1998 Academic Press.

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.

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.

The high resolution (0.014 A in the range 2000-1500 A) investigation of quasilinear spectra observed with NO in Ne or Ar matrices below 2000 A provides useful information about various types of interactions of the molecule with the host crystal. Some features obtained are discussed in terms of a static interaction which leads to the washing out of the Rydberg transitions. The dynamic interaction is revealed through spectral features which reflect the phonon density of states of the matrix as well as through features correlated to libration in the site.

Medium resolution spectra of molecules subjected to a pressure of argon indicate a broadening and a shift of Rydberg transitions, dependent on the shape of the outer orbital. Valence transitions are comparatively little affected even at 200 bar. In the case of the very complicated spectrum of NO, the washing out of the Rydberg bands allows the valence bands to show up even at a moderate pressure, so that the spectrum tends toward the spectrum of NO isolated in a solid rare gas matrix, from which spectrum discrete Rydberg bands are absent. Vibronic terms in homogeneous interaction behave, under pressure, in a way which reflects closely their degree of interaction in the free molecule.

Previous low resolution studies indicated that, in the absorption spectrum, transitions to Rydberg states are far more sensitive to pressure than transitions to valence states in accordance with the complete vanishing of Rydberg bands and the deperturbation of the valence bands in the spectrum of NO trapped in a solid rare gas matrix. The present study of NO is the first extensive investigation of medium and high resolution molecular electronic spectra subjected to pressure of foreign gases. It is observed that, at the highest pressure attained (∼1000 bar), almost all of the Rydberg bands have vanished whereas the remaining valence bands stay relatively sharp. While high pressure medium resolution spectra give information about the deperturbation of intensities and of vibrational spacings of the valence bands, inspection of low pressure high resolution spectra reveals that the rotational lines react to pressure in a way reflecting closely the degree of configuration mixing between Rydberg and valence states.

Five new emission bands have been analyzed at high resolution in the short wavelength range of the vacuum ultraviolet emission spectrum of molecular nitrogen. Four of them are assigned to the band system c′ 6 1 Σ u + (v′ = 0) → X 1 Σ g + (v″ = 0–3) . The fifth band, at 82.6562 nm, corresponds to a transition from a highly excited state which was not known before but which is presently detected also in absorption at high resolution in 14N2 and 15N2. The new state is of 1Σu+ symmetry and is identified as the first term of a Rydberg series converging toward the A2Πu state of N2+. Both excited electronic states lie above the limit of dissociation of N2 into N( 2 D) + N( 2 D) . They are the only states in this energy range which are not totally predissociated.

The complete high resolution emission spectrum of molecular hydrogen is obtained for the first time in the range 78–118 nm. A uniform set of data is derived from accurate line positions of the (unperturbed) Q branches of the C, D, D′, and [Formula: see text] transitions. Molecular constants fitted for both the ground state and the excited states of symmetry [Formula: see text] are obtained. For the latter case, they are compared with ab initio and multichannel quantum defect theory (MQDT) calculations. Self-absorption features indicate the production, in an appreciable amount, of H2(ν″ = 1) in the discharge. The reported data were not available to laser physicists and also astrophysicists who have observed strong emission lines of H2 from the atmospheres of Jupiter and Saturn.

A l'aide d'une lampe a decharge a basse pression, mise en evidence de nouvelles bandes de N 2 en UV extreme, avec des indices de predissociation d'apres les modifications de la structure rotationnelle de quelques bandes correspondant a des transitions provenant d'un etat electronique different dans 14 N 2 et 15 N 2

A comparison of the dimensions of the trapping site in solid Xe, Kr, Ar and Ne to that in solid N2 leads to new assignments for the vibrational terms of the B3Σu−←X3Σg− transition of the oxygen molecule trapped in matrices. The anomalous shape previously found, in the argon matrix, for the potential energy curve of the excited state B3Σu− is corrected. The Lennard—Jones intermolecular potential parameters are derived for this excited state.

The progression observed below 1000 \AA{} in spectra of solid ${\mathrm{N}}_{2}$, pure and trapped in Ne and C${\mathrm{F}}_{4}$ matrices at 4.2 K, is ascribed to the valence transition $b^{1}\ensuremath{\Pi}_{\mathrm{u}}\ensuremath{\leftarrow}X^{1}\ensuremath{\Sigma}_{\mathrm{g}}^{+}$ of ${\mathrm{N}}_{2}$. As previously observed in the similar case of NO, the regularity in intensity distribution and in vibrational spacings indicates the absence of the Rydberg transition $c^{1}\ensuremath{\Pi}_{\mathrm{u}}\ensuremath{\leftarrow}X^{1}\ensuremath{\Sigma}_{\mathrm{g}}^{+}$ responsible for strong perturbations in the free-molecule spectrum.

The ultraviolet spectra of CS 2 and OCS trapped in a rigid matrix have been observed. The possibility of appearance of Rydberg transitions is discussed in terms of the dimension of the excited orbital and the matrix lattice.

The experimental data, previously reported, regarding the electronic transitions of matrix isolated CO, N 2 , and NO are qualitatively related to the site dimension. The magnitude of the perturbation depends essentially on the nature of the transition or, in other words, on the dimension of the excited orbital. Valence transitions are modified very little whereas Rydberg transitions are strongly affected. The problem of rotation in solid is approached and the orientation of N 2 in neon is deduced from the aspect of the spectrum.

Several absorption spectra are presented which were taken in the spectral range 2600-1050 A with atoms (Hg, Xe), radical (H) and molecules (CO, N 2 , NO) in pure solid form or trapped in solid rare gas matrices at temperatures between 20 and 1.5°K. Shifts of resonance lines of Hg and Xe are compared with those obtained under high pressure in gaseous state. The fourth positive group of CO and the Lyman-Birge-Hopfield bands of N 2 are perturbed in the pure solid but not in matrices. The intensity of the w 1 Δ u ← X 1 Σ g + transition of N 2 is enhanced in the pure solid but not in matrix and the progression is observed up to v ′ = 17. Rydberg states disappear in solid dilute NO and vibrational spacings of the valence states become regular as the perturbating interactions of the two types of states no longer exist.

An attempt is made to use the Lennard-Jones intermolecular potential parameters, derived from matrix shifts, to predict the position of pressure-induced satellites of spectral lines. Comparison with experiment shows that a simple Lennard-Jones model is inadequate when one of the pair of interacting particles is in an excited electronic state. This result supports Jefimenko's assumption of a deformation of the potential curve at medium intermolecular distances.

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.

A clean demountable dye cell is described which is more advantageous than the usual commercial cuvettes for obtaining good quality light beams from pulsed dye lasers.

The absorption spectrum of solid thin films of neon has been recorded at 4.2 K in the photon energy range from 15 to 25 eV. The first three terms of the hydrogenic series, corresponding to the resonance doublet of the free atom, have been identified and the energy gap at the $\ensuremath{\Gamma}$ point is calculated to be 21.42 eV.