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Context. Highly excited molecular hydrogen H2 has been observed in many regions of shocked molecular gas. A recently published $K$-band spectrum of Herbig-Haro 7 (HH7) contains several vibration-rotation lines of H2 from highly excited energy levels that have not been detected elsewhere, including a line at 2.179 $\mu$m identified as arising from the $v$=2 $J$=29 level, which lies above the dissociation limit of H2. One emission line at 2.104 $\mu$m in this spectrum was unidentified. Aims. We aim to complete the analysis of the spectrum of HH7 by including previously missing molecular data that have been recently computed. Methods. We re-analysed the $K$-band spectrum, emphasising the physics of quasi-bound upper levels that can produce infrared emission lines in the $K$ band. Results. We confirm the identification of the $2-1$ $S$(27) line at 2.1785 $\mu$m and identify the line at 2.1042 $\mu$m as due to the 1-0 $S$(29) transition of H2, whose upper level energy is also higher than the dissociation limit. This latter identification, its column density, and the energy of its upper level further substantiate the existence of a hot thermal component at 5000 K in the HH7 environment.} Conclusion. The presence of the newly identified $1-0$ $S$(29) line, whose quasi-bound upper level ($v$=1, $J$=31) has a significant spontaneous dissociation probability, shows that dissociation of H2 is occurring. The mechanism by which virtually all of the H2 levels with energies from 20,000 K to 53,000 K is maintained in local thermodynamic equilibrium at a single temperature of $\sim$5,000 K remains to be understood., Comment: 5 pages, 3 figures, accepted in Astronomy and Astrophysics Letters 22/12/2022

Recently we published an accurate analysis of molecular hydrogen absorption in the photospheres of the white dwarf stars GD133 and GD29-38, previously observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. Constraints were derived on a possible dependence of the proton-electron mass ratio on gravitational fields that are 10 000 times stronger than at the Earth's surface. Here we present further details of that study, in particular a re-evaluation of the spectrum of the B1∑+u - X1∑+g (v1, vn) Lyman bands relevant for the prevailing temperatures (12 000-14 000 K) of the photospheres. The emphasis is on the calculation of so-called Ki-coefficients, that represent the sensitivity of each individual line to a possible change in the proton-electron mass ratio. Such calculations were performed by semi-empirical methods and by ab initio methods providing accurate and consistent values. A full listing is provided for the molecular physics data on the Lyman bands (wavelengths λi, line oscillator strengths fi, radiative damping rates λi, and sensitivity coefficients Ki) as required for the analyses of H2-spectra in hot dwarf stars. A similar listing of the molecular physics parameters for the C1πu - X1∑+g (v1, vn) Werner bands is provided for future use in the analysis of white dwarf spectra.

The high spectral resolution R about 45,000 provided by IGRINS (Immersion Grating INfrared Spectrometer) at MacDonald Observatory and R 100,000 achieved by CRIRES (CRyogenic high-resolution InfraRed Echelle Spectrograph) at VLT (Very Large Telescope) challenges the present knowledge of infrared spectra. aims We aim to predict the full infrared spectrum of molecular hydrogen at a comparable accuracy. methods We take advantage of the recent theoretical ab initio studies on molecular hydrogen to compute both the electric quadrupole and magnetic dipole transitions taking place within the ground electronic molecular state of hydrogen. results We computed the full infrared spectrum of molecular hydrogen at an unprecedented accuracy and derive for the first time the emission probabilities including both electric quadrupole ($\Delta J = 0, \pm$2) and magnetic dipole transitions ($\Delta J = 0$) as well as the total radiative lifetime of each rovibrational state. Inclusion of magnetic dipole transitions increases the emission probabilities by factors of a few for highly excited rotational levels, which occur in the 3-20 $\mu$ range}, Comment: 6 pages, 1 figure, 2 tables. Full Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/630/A58. It can also be obtained on request to evelyne.roueff@obspm.fr

Energies and probabilities of Lyman transitions of high rovibrationally excited H 2 , HD and D 2 molecules have been measured and compared with calculations. The experimental results are obtained from laser-induced fluorescence spectra that have been recorded in the spectral range from 60 500 to 83 500 cm −1 , covering 2/3 of the hydrogen Lyman band system. The necessary vacuum-UV radiation is produced by stimulated anti-Stokes Raman scattering, providing a widely tunable radiation source with narrow spectral bandwidth to resolve single Lyman transitions. The highest internal energies of detected hydrogen isotopologues are close to the dissociation limit. This extends the available data base of Lyman transitions from and to higher rotational states ( J > 10) of HD and D 2 .

At high resolving power -->(?/? ? ? 10,000) , we have measured the electron impact-induced fluorescence spectrum of H2 from 3300-10000 ? at 20 and 100 eV. We have analyzed the visible-optical-near-IR (VOIR) emission spectrum under optically thin, single-scattering experimental conditions. The high-resolution spectrum contains transitions from the gerade Rydberg series of singlet states to the ungerade series of Rydberg states ( -->EF1?g+, -->GK1?g+, --> H1?g+, -->I1?g, -->J1?g... ? B1?u+, -->C1?u, -->B'1?u+, -->D1?u) and the Rydberg series of triplet states dominated by -->d3?u, -->k3?u, -->j3?g? a3?g+ band systems. A model VOIR spectrum of H2 from 7500 to 10000 ?, based on newly calculated transition probabilities and line positions including rovibrational coupling for singlet gerade states, is in excellent agreement with the observed intensities. The rotational line emission cross sections for direct excitation of the singlet states at 100 eV and triplet states at 20 eV were measured. The absolute cross section values for excitation to the singlet gerade states at 100 eV was measured to be -->(4.58 ? 1.37) ? 10?18 cm2; the excitation cross section to the triplet states at 20 eV was found to be -->(1.38 ? 0.41) ? 10?18 cm2. The singlet gerade emission cross sections are the cascading cross sections to the UV spectrum (including the Lyman and Werner band systems) and the triplet state emission cross sections are the cascade dissociation cross sections of the H2 -->(a3?g+?b3?u+) continuum for the production of fast hydrogen atoms. Electrons are also effective in exciting high vibrational levels belonging to ungerade symmetry (B, B', C, D) which subsequently emit toward gerade symmetry states in the VOIR domain. Strong emission from the ungerade-gerade transitions are observed from 7300 to 7400 ?.

In this paper, we derive the theoretical properties of rovibrational levels belonging to excited B, C, B' , and D electronic states of HD. We compute the eigenvalues and eigenfunctions of the nuclear coupled Schroedinger equations using ab initio electronic molecular properties available in the literature. Transition wavenumbers and spontaneous emission probabilities are calculated for all transitions belonging to B-X, C-X, B' -X, and D-X electronic band systems of HD when the upper rotational quantum number is below or equal to 10. We compare our results with available experimental values: the accuracy in the wavenumbers is on the order of 3 reciprocal centimetres, whereas the intensity properties are satisfactorily reproduced. The origin of the remaining discrepancies is analyzed.

High-resolution ( ∼ 0.22 A ) spectra of the north jovian aurora were obtained in the 905–1180 A window with the Far Ultraviolet Spectroscopic Explorer (FUSE) on October 28, 2000. The FUSE instrument resolves the rotational structure of the H2 spectra and the spectral range allows the study of self-absorption. Below 1100 A, transitions connecting to the v ″ ⩽ 2 levels of the H2 ground state are partially or totally absorbed by the overlying H2 molecules. The FUSE spectra provide information on the overlying H2 column and on the vibrational distribution of H2. Transitions from high-energy H2 Rydberg states and treatment of self-absorption are considered in our synthetic spectral generator. We show comparisons between synthetic and observed spectra in the 920–970, 1030–1080, and 1090–1180 A spectral windows. In a first approach (single-layer model ), the synthetic spectra are generated in a thin emitting layer and the emerging photons are absorbed by a layer located above the source. It is found that the parameters of the single-layer model best fitting the three spectral windows are 850, 800, and 800 K respectively for the H2 gas temperature and 1.3 × 10 18 , 1.5 × 10 20 , and 1.3 × 10 20 cm − 2 for the H2 self-absorbing vertical column respectively. Comparison between the H2 column and a 1-D atmospheric model indicates that the short-wavelength FUV auroral emission originates from just above the homopause. This is confirmed by the high H2 rovibrational temperatures, close to those deduced from spectral analyses of H+3 auroral emission. In a second approach, the synthetic spectral generator is coupled with a vertically distributed energy degradation model, where the only input is the energy distribution of incoming electrons (multi-layer model ). The model that best fits globally the three FUSE spectra is a sum of Maxwellian functions, with characteristic energies ranging from 1 to 100 keV, giving rise to an emission peak located at 5 μbar, that is ∼ 100 km below the methane homopause. This multi-layer model is also applied to a re-analysis of the Hopkins Ultraviolet Telescope (HUT) auroral spectrum and accounts for the H2 self-absorption as well as the methane absorption. It is found that no additional discrete soft electron precipitation is necessary to fit either the FUSE or the HUT observations.

The electron impact emission function of the P(3) branch for the (0, 4) band of the H2 B 1? u+?X 1? g+ band system has been measured from threshold to 1800 eV. The emission function exhibits structure indicating strong contributions from both resonance and non-resonance excitation. The non-resonance component contains direct and cascade contributions. A combination of experimental and theoretical considerations permits separation of resonance, dipole-allowed direct, dipole-allowed indirect, and dipole-forbidden excitation components for the Jj = 2, vj = 0 level of the B 1? u+ state. An effective excitation function for the EF 1? g+?X 1? g+ band system has been obtained from a nonlinear least-squares analysis of the dipole-forbidden component of the B 1? u+ state emission function. The absolute value of EF 1? g+?X 1? g+ cross section is established on the basis of earlier experimental results of Liu et al 1995 Astrophys. J. Suppl. 101 375?99 and 2002 Astrophys J. Suppl. 138 229?45 and Abgrall et al 1997 Astrophys. J. 481 557?66 and 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3813?38. A near-threshold apparent resonance excitation cross section of (8.1 ? 3.2) ? 10?18 cm2 is obtained for the B 1? u+ (Jj = 2 and vj = 0). An EF 1? g+?X 1? g+ Born cross section has been calculated from the electronic form factor of Kolos et al 1982a J. Chem. Phys. 77 1335?44. Analysis shows that the Born asymptotic shape function of the EF 1? g+?X 1? g+ band system starts at ~400 eV, a significantly higher energy than previously expected. The excitation function is especially important for interpreting outer planet atmospheric dayglow and auroral activity and can be used to infer energy deposition and heating rates.

Medium-resolution (full width at half-maximum Δλ = 0.5 A) vacuum ultraviolet (VUV) emission spectra of H2 from forbidden excitation to the excited singlet-gerade states and subsequent cascade to the singlet-ungerade states have been studied with a time-resolved electron-impact technique. Emissions from the B 1Σ, C 1Πu, B' 1Σ, and D 1Πu states that are entirely due to cascade from the singlet-gerade states have been observed. Lyman band emission intensities dominate over the entire 940-1650 A wavelength region, though Werner band emission intensities are also significant. In addition, very weak cascade emissions from the vj = 0 and 1 levels of the B' 1Σ and D 1Πu states are also evident. In contrast to previous assumption, the cascade excitation is observed to take place over all the vibrational levels of the B 1Σ and C 1Πu states, while contributing heavily to low vj levels of the B 1Σ state. Synthetic spectra based on the calculated transition probabilities of the EF 1Σ, GK 1Σ, H 1Σ, I 1Πg, J 1Δg, O 1Σ and P 1ΣB 1Σ, C 1Πu, B' 1Σ, and D 1Πu band systems and Franck-Condon factors of the EF 1Σ-X 1Σ, GK 1Σ-X 1Σ, H 1Σ-X 1Σ, I 1Πg-X 1Σ, J 1Δg-X 1Σ, O 1Σ-X 1Σ, and P 1Σ-X 1Σ are in good agreement with the observed Lyman and Werner band intensities. The present study shows that a number of singlet-gerade and singlet-ungerade states are involved in the cascade excitation process of H2. The cascade from these states in the VUV provide diagnostic information on astrophysical sources for H2 emission.

Following the recent detection of an auroral signal on Uranus (Lamy et al. [2012]. Geophys. Res. Lett. 39, 7105) during HST/STIS observation performed in November 2011, we analyzed the associated HST/STIS FUV spectral images obtained in 2011 and 2012. Our purpose was to extract any possible H2 emission produced in the upper atmosphere of the planet. To interpret these data, we adapted a version of the kinetic Trans* code to the Uranian case. This code simulates the H2 emissions created by energetic particle precipitations in the upper atmosphere. The signal measured in the 1330-1700 A range, of around 1.8 kR, is composed mostly of reflected sunlight with a small contribution from upper atmospheric emissions. For most spectra, we found no evidence of particle precipitation, indicating a precipitation flux smaller than 0.01 erg cm-2 s-1. For the spectrum of 29 November 2011 however, when an auroral spot was positively detected, we additionally identified a small contribution of H2 emission which requires a precipitating energy flux up to 0.05 erg cm-2 s-1. This study also establishes that the Hubble Space Telescope (HST) can be used to monitor the aurorae on Uranus in its image and spectral modes, and to estimate the associated precipitated energy flux, provided a very careful data processing is applied. (Less)

The total radiative transition probabilities of rovibronic levels of B, C, B 0 and D states of molecular hydrogen are calculated with emphasis on the dissocia- tion fraction and the kinetic energy released in the con- tinuum radiation process. The mixing percentages of B, C, B 0 and D adiabatic states are also given. The data are calculated with the detailed transition probabilities ob- tained by Abgrall et al. (1993, 1994). We have included, in the present analysis, results obtained by using a recent ab initio transition moment for D X which comprises a larger range of internuclear distances. The related data on individual transition probabilities may be obtained on request.

The high-resolution (full width at half maximum = 0.11 A) emission spectrum of the deuterium molecule produced by electron-impact excitation at 100 eV has been measured in the wavelength range 1200 - 1660 A. In conjunction with the experimental measurement, transition probabilities of and D band systems are calculated. Synthetic spectra based on the calculated transition probabilities are in very good agreement with the optically thin experimental spectra. While centrifugal effects on the overall Lyman band emission intensity in D2 and H2 are similar, the effect of rotation-vibrational perturbations between the B 1u+ and C 1u+ states on spectral intensities is found to be less significant in D2. Excitations via isotropic ( J = 0) and anisotropic ( J = ±2, and 0) interactions for the dipole forbidden E, F 1g+-X 1g+ transition are inferred from the measured spectra. Excitation cross sections of the B 1u+-X 1g+ and C 1u-X 1g+ bands, along with the estimated E, F 1g+-B 1u+ cascade cross section, for D2 are obtained.

The emission continua of the dissociative transitions B 1Σ+u-X 1Σ+g, B 1Σ+u-X 1Σ+g, C 1Πu-X 1Σ+g, and D 1Πu-X 1Σ+g of molecular hydrogen have been calculated. Synthetic spectra of H2 are in excellent agreement with high-resolution electron-impact-induced emission spectra obtained at 100 eV. An improved calibration standard is obtained, and the dissociation yields of the Lyman and Werner continua produced by electron-impact excitation are presented.

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 effects of rotational-vibrational interaction, and of rotational coupling between the {ital B} 2{ital p} {sup 1}{Sigma}{sub {ital u}}{sup +} and {ital C} 2{ital p} {sup 1}{Pi}{sub {ital u}} electronic states, on the {ital B}--{ital X} fluorescence continuum of H{sub 2} associated with spontaneous dissociation were investigated spectroscopically using monochromatized synchrotron radiation for selective excitation of rovibronic states. The rotational shifts and perturbations in the modulated continua intensities observed agree well with close-coupling and Jeffreys-Wentzel-Kromers-Brillouin (JWKB) calculations also performed, and are explained in terms of nonadiabatic coupling effects and rainbow-interference structures. A straightforward experimental technique is described to detect mixed electronic states.

The effects of rotation-vibration interaction and of rotational coupling between the B 2p 1Σu+ and C 2p 1Πu electronic states on the B-X continuum of H2 were investigated spectroscopically using monochromatized synchrotron radiation for selective excitation of rovibronic states. The perturbed continuum intensities observed for the first time agree well with close-coupling calculations also performed.

We discuss the dissociation of a molecule HXD, when the dissociation occurs on a repulsive surface with a single saddle point. We calculate the order of magnitude of the intramolecular isotope effect, and find it in agreement with experimental observations.

Recent work on radiative processes and collisional excitation in molecular Hydrogen and its deuterated isotopic substitute and in molecular Carbon is reviewed. Particular attention is drawn to non-adiabatic coupling effects on the intensities of Lyman and Werner band systems of the vacuum ultraviolet spectrum of H2 and to the role of nuclear spin on ortho-para transitions in H2 due to H+ collisions. The inter-relation between those processes and state to state chemistry is stressed out. We discuss the implications of these new data in a recent comprehensive model of diffuse interstellar clouds (Viala et al., 1987).

Absorption lines of H$_2$ and HD molecules observed at high redshift in the line of sight towards quasars are a test ground to search for variation of the proton-to-electron mass ratio $\mu$. For this purpose, results from astronomical observations are compared with a compilation of molecular data of the highest accuracy, obtained in laboratory studies as well as in first-principles calculations. Aims: A comprehensive line list is compiled for H$_2$ and HD absorption lines in the Lyman ($B^1\Sigma_u^+$ - $X^1\Sigma_g^+$) and Werner ($C^1\Pi_u$ - $X^1\Sigma_g^+$) band systems up to the Lyman cutoff at 912 Angstroms. Molecular parameters listed for each line $i$ are the transition wavelength $\lambda_i$, the line oscillator strength $f_i$, the radiative damping parameter of the excited state $\Gamma_i$, and the sensitivity coefficient $K_i$ for a variation of the proton-to-electron mass ratio. Methods: The transition wavelengths $\lambda_i$ for the H$_2$ and HD molecules are determined by a variety of advanced high-precision spectroscopic experiments involving narrowband vacuum ultraviolet lasers, Fourier-transform spectrometers, and synchrotron radiation sources. Results for the line oscillator strengths $f_i$, damping parameters $\Gamma_i$, and sensitivity coefficients $K_i$ are obtained in theoretical quantum chemical calculations. Results: A new list of molecular data is compiled for future analyses of cold clouds of hydrogen absorbers, specifically for studies of $\mu$-variation from quasar data. The list is applied in a refit of quasar absorption spectra of B0642$-$5038 and J1237$+$0647 yielding constraints on a variation of the proton-to-electron mass ratio $\Delta\mu/\mu$ consistent with previous analyses., Comment: 4 pages. Accepted by Astronomy and Astrophysics. The 3 tables containing the molecular data are available at http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/A+A/622/A127 and are contained in the source package of the arXiv submission (in "Other formats")