Extreme ultravioletϩultraviolet ͑XUVϩUV͒ two-photon ionization spectra of the b 1 ⌸ u (v ϭ0-9), c 3 1 ⌸ u (vϭ0,1), o 1 ⌸ u (vϭ0,1), c 4 Ј 1 ⌺ u ϩ (vϭ1) and bЈ 1 ⌺ u ϩ (vϭ1,3-6) states of 15 N 2 were recorded with a resolution of 0.3 cm Ϫ1 full-width at half-maximum ͑FWHM͒. In addition, the b 1 ⌸ u (vϭ1,5-7) states of 14 N 15 N were investigated with the same laser source. Furthermore, using an ultranarrow bandwidth XUV laser ͓ϳ250 MHz (ϳ0.01 cm Ϫ1) FWHM͔, XUVϩUV ionization spectra of the b 1 ⌸ u (vϭ0-1,5-7), c 3 1 ⌸ u (vϭ0), o 1 ⌸ u (vϭ0), c 4 Ј 1 ⌺ u ϩ (vϭ0), and bЈ 1 ⌺ u ϩ (v ϭ1) states of 15 N 2 were recorded in order to better resolve the band-head regions. For 14 N 15 N, ultrahigh resolution spectra of the b 1 ⌸ u (vϭ0-1,5-6), c 3 1 ⌸ u (vϭ0), and bЈ 1 ⌺ u ϩ (vϭ1) states were recorded. Rotational analyses were performed for each band, revealing perturbations arising from the effects of Rydberg-valence interactions in the 1 ⌸ u and 1 ⌺ u ϩ states, and rotational coupling between the 1 ⌸ u and 1 ⌺ u ϩ manifolds. Finally, a comprehensive perturbation model, based on the diabatic-potential representation used previously for 14 N 2 , and involving diagonalization of the full interaction matrix for all Rydberg and valence states of 1 ⌺ u ϩ and 1 ⌸ u symmetry in the energy window 100 000-110 000 cm Ϫ1 , was constructed. Term values for 15 N 2 and 14 N 15 N computed using this model were found to be in good agreement with experiment.

No abstract

The emission spectrum of the D(2) molecule has been studied at high resolution in the vacuum ultraviolet region 78.5-102.7 nm. A detailed analysis of the two D (1)Pi(u)-->X (1)Sigma(g) (+) and D(') (1)Pi(u) (-)-->X (1)Sigma(g) (+) 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 D (1)Pi(u) state with the lowest electronic states B (1)Sigma(u) (+), C (1)Pi(u), and B(') (1)Sigma(u) (+). 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 probably due to nonadiabatic couplings with other higher electronic states which were neglected in the calculations.

The strong electronic absorption systems of the B 1 u ÿ X 1 g Lyman and the C 1 u ÿ X 1 g Werner bands can be used to probe possible mass-variation effects on a cosmological time scale from spectra observed at high redshift, not only in H 2 but also in the second most abundant hydrogen isotopomer HD. High resolution laboratory determination of the most prominent HD lines at extreme ultraviolet wavelengths is performed at an accuracy of = 5 10 ÿ8 , forming a database for comparison with astrophysical data. Sensitivity coefficients K i d ln i =d ln are determined for HD from quantum ab initio calculations as a function of the proton-electron mass ratio . Strategies to deduce possible effects beyond first-order baryon/lepton mass ratio deviations are discussed. DOI: 10.1103/PhysRevLett.100.093007 PACS numbers: 33.20.ÿt, 06.20.Jr, 95.30.Dr, 98.80.Bp The observation of spectral features at high redshift (z 2-3) provides an opportunity to probe minute variations of some fundamental constants over time intervals of 10 10 years, corresponding to 80% of the lifetime of the Universe. For the fine structure constant evidence has been reported for a temporal drift at 5 significance [1]. Variation of another fundamental constant, the dimensionless proton-electron mass ratio m p =m e , may be probed through spectra of molecules. Recently, an indication for a possible decrease of was reported at = 2:45 0:59 10 ÿ5 over a time interval of 12 10 9 years [2,3]. This result is derived from a set of 76 H 2 spectral lines in two absorption systems at z 2:59 and z 3:02 in the line of sight towards quasars Q0405 ÿ 443 and Q0347 ÿ 383 [4]. From observations of the NH 3 inversion splitting in the astrophysical object B0218 357 at z 0:68, a tight constraint upon variation at = 0:6 1:9 10 ÿ6 was deduced [5]. These seemingly contradictory results might be reconciled by invoking the concept of a phase transition having occurred at z 1, transiting from a matter-dominated to a darkenergy-dominated Universe; variation of constants is hypothesized to occur only before the phase transition, henceThe comparison of spectral lines over cosmological time scales depends on the availability of spectral transitions that can be observed at high accuracy and at high redshift. Molecular hydrogen is the most abundant molecule in the Universe by orders of magnitude. The abundance of the deuterated HD species competes with other abundant molecules such as CO and CH such that it is worthwhile to consider the opportunity of using HD absorption for probing mass-variation effects. HD lines in the Lyman bands have indeed been observed in the object Q1232 082 at z 2:34 [7].To facilitate this opportunity, a set of highly accurate zero-redshift (laboratory) transition wavelengths of HD electronic absorption lines is required. Here we report on the spectral calibration of zero-redshift HD lines in the B 1 u ÿ X 1 g Lyman and the C 1 u ÿ X 1 g Werner bands, referred to as Lv and Wv bands with v the vibrational quantum number, in the extreme ultraviolet range 100-11...

Tungsten spectra excited in the vacuum sparks of different setups and electric circuits were recorded on two high-resolution vacuum spectrographs. For the region 190-500 Å, a 10 m normal incidence spectrograph with a 3600 lines/mm grating was used in the Meudon Observatory. In the region below 350 Å, a set of spectra was produced using a 3 m grazing incidence spectrograph with a 3600 lines/mm grating in the Institute of Spectroscopy in Troitsk. A total of 187 lines in the region 160-271 Å were identified as transitions to the low-lying odd configurations 4f 13 5s 2 5p 6 and 4f 14 5s 2 5p 5 from the interacting excited even 4f 12 5s 2 5p 6 5d + 4f 13 5s 2 5p 5 (5d + 6s) + 4f 14 5s 2 5p 4 (5d + 6s) + 4f 14 5s5p 6 configurations. It was found that 4f 13 5s 2 5p 6 2 F 7/2 is the ground level of W VIII. The fine structure splitting and relative positions of the odd terms were established, and 98 levels of the excited even configurations were found.

The 3pπD (1)Π(u) state of the H(2) molecule was reinvestigated with different techniques at two synchrotron installations. The Fourier transform spectrometer in the vacuum ultraviolet wavelength range of the DESIRS beamline at the SOLEIL synchrotron was used for recording absorption spectra of the D (1)Π(u) state at high resolution and high absolute accuracy, limited only by the Doppler contribution at 100 K. From these measurements, line positions were extracted, in particular, for the narrow resonances involving (1)Π(u) (-) states, with an accuracy estimated at 0.06 cm(-1). The new data also closely match multichannel quantum defect calculations performed for the Π(-) components observed via the narrow Q-lines. The Λ-doubling in the D (1)Π(u) state was determined up to v=17. The 10 m normal incidence scanning monochromator at the beamline U125/2 of the BESSY II synchrotron, combined with a home-built target chamber and equipped with a variety of detectors, was used to unravel information on ionization, dissociation, and intramolecular fluorescence decay for the D (1)Π(u) vibrational series. The combined results yield accurate information on the characteristic Beutler-Fano profiles associated with the strongly predissociated Π(u) (+) parity components of the D (1)Π(u) levels. Values for the parameters describing the predissociation width as well as the Fano-q line shape parameters for the J=1 and J=2 rotational states were determined for the sequence of vibrational quantum numbers up to v=17.

The strong interaction between the B 3sσ 1Σ+ Rydberg state and the D′ 1Σ+ valence state of the CO molecule is shown to cause large changes in the vibrational and rotational constants of the B state, as well as predissociation of all rotational levels of B (v′=2) and a breaking off in the emission of B (v′=1) levels at J=36 in 12C 16O and J=37 in 13C 16O. A two-state diabatic model of the Rydberg–valence interaction is constructed and vibrational term values, widths, and intensities are calculated by close coupling in order to account for the strong mixing. The model separates the differences between the spectroscopic constants of the B state and those of the ground state molecular ion into two components, one due to the R-dependent quantum defect of the B state and another due to the strong Rydberg–valence perturbation. The perturbation is characterized by a constant coupling matrix element of 2900 cm−1 inside the crossing point of the two diabatic potentials, decaying to zero at long internuclear distances. Basically good agreement is found between the model and experiment for shifts in vibrational and rotational terms and for predissociation widths and relative band intensities. The second breaking off in emission in the B (v′=1) rotational series is used to estimate the height of the long-range barrier maximum in the D′ 1Σ+ state to be about 1048±19 cm−1 above the ground state dissociation limit. Comparison of predicted widths from the two channel close coupled model with those from a single channel adiabatic model shows differences on the order of a factor of 2.

The D 1 Πu -X 1 Σ + g absorption system of molecular deuterium has been re-investigated using the VUV Fourier -Transform (FT) spectrometer at the DESIRS beamline of the synchrotron SOLEIL and photon-induced fluorescence spectrometry (PIFS) using the 10 m normal incidence monochromator at the synchrotron BESSY II. Using the FT spectrometer absorption spectra in the range 72 -82 nm were recorded in quasi static gas at 100 K and in a free flowing jet at a spectroscopic resolution of 0.50 and 0.20 cm −1 respectively . The narrow Q-branch transitions, probing states of Π − symmetry, were observed up to vibrational level v = 22. The states of Π + symmetry, known to be broadened due to predissociation and giving rise to asymmetric Beutler-Fano resonances, were studied up to v = 18. The 10 m normal incidence beamline setup at BESSY II was used to simultaneously record absorption, dissociation, ionization and fluorescence decay channels from which information on the line intensities, predissociated widths, and Fano q-parameters were extracted. R-branch transitions were observed up to v = 23 for J = 1-3 as well as several transitions for J = 4 and 5 up to v = 22 and 18 respectively. The Q-branch transitions are found to weakly predissociate and were observed from v = 8 to the final vibrational level of the state v = 23. The spectroscopic study is supported by two theoretical frameworks. Results on the Π − symmetry states are compared to ab initio multi-channel-quantum defect theory (MQDT) calculations, demonstrating that these calculations are accurate to within 0.5 cm −1 . Furthermore, the calculated line intensities of Q-lines agree well with measured values. For the states of Π + symmetry a perturbative model based on a single bound state interacting with a predissociation continuum was explored, yielding good agreement for predissociation widths, Fano q-parameters and line intensities.