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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.

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 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.