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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−.

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.

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.

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.

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

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 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.

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 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.