G.D. Dickenson

Fundamental Vibration of Molecular Hydrogen

The fundamental ground tone vibration of H(2), HD, and D(2) is determined to an accuracy of 2×10(-4) cm(-1) from Doppler-free laser spectroscopy in the collisionless environment of a molecular beam. This rotationless vibrational splitting is derived from the combination difference between electronic excitation from the X(1)Σ(g)(+), v=0, and v=1 levels to a common EF(1)Σ(g)(+), v=0 level. Agreement within 1σ between the experimental result and a full ab initio calculation provides a stringent test of quantum electrodynamics in a chemically bound system.

QED Effects in Molecules: Test on Rotational Quantum States of H(2)

Quantum electrodynamic effects have been systematically tested in the progression of rotational quantum states in the X 1Σ(g)(+), v=0 vibronic ground state of molecular hydrogen. High-precision Doppler-free spectroscopy of the EF 1Σ(g)(+)-X 1Σ(g)(+) (0,0) band was performed with 0.005  cm(-1) accuracy on rotationally hot H2 (with rotational quantum states J up to 16). QED and relativistic contributions to rotational level energies as high as 0.13  cm(-1) are extracted, and are in perfect agreement with recent calculations of QED and high-order relativistic effects for the H2 ground state.

High resolution Fourier-transform extreme ultraviolet photoabsorption spectroscopy of 14N15N

The first comprehensive high-resolution photoabsorption spectrum of (14)N(15)N has been recorded using the Fourier-transform spectrometer attached to the Desirs beamline at the Soleil synchrotron. Observations are made in the extreme ultraviolet and span 100 000-109 000 cm(-1) (100-91.7 nm). The observed absorption lines have been assigned to 25 bands and reduced to a set of transition energies, f values, and linewidths. This analysis has verified the predictions of a theoretical model of N(2) that simulates its photoabsorption and photodissociation cross section by solution of an isotopomer independent formulation of the coupled-channel Schrödinger equation. The mass dependence of predissociation linewidths and oscillator strengths is clearly evident and many local perturbations of transition energies, strengths, and widths within individual rotational series have been observed.

Synchrotron vacuum ultraviolet radiation studies of the D(1)Pi(u) state of H(2)

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.

Fourier-transform spectroscopy of HD in the vacuum ultraviolet at lambda = 87-112 nm

Absorption spectroscopy in the vacuum ultraviolet (VUV) domain was performed on the hydrogen-deuteride molecule with a novel Fourier-transform spectrometer based upon wavefront division interferometry. This unique instrument, which is a permanent endstation of the undulator-based beamline DESIRS on the synchrotron SOLEIL facility, opens the way to Fourier-transform spectroscopy in the VUV range. The HD spectral lines in the Lyman and Werner bands were recorded in the 87–112 nm range from a quasi-static gas sample in a windowless configuration and with a Doppler-limited resolution. Line positions of some 268 transitions in the Lyman bands and 141 transitions in the Werner bands were deduced with uncertainties of 0.04 cm−1 (1σ) which correspond to Δλ/λ ∼ 4 × 10−7. This extensive laboratory database is of relevance for comparison with astronomical observations of H2 and HD spectra from highly redshifted objects, with the goal of extracting a possible variation of the proton-to-electron mass ratio (μ = m p /m e ) on a cosmological time scale. For this reason also calculations of the so-called sensitivity coefficients K i were performed in order to allow for deducing constraints on Δμ/μ. The K i coefficients, associated with the line shift that each spectral line undergoes as a result of a varying value for μ, were derived from calculations as a function of μ solving the Schrödinger equation using ab initio potentials.

VUV spectroscopic study of the D1Piu state of molecular deuterium

The D 1Π u – 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.

VUV spectroscopic study of the B '' (B)over-bar(1) Sigma(+)(u) state of H-2

Spectral lines, probing rotational quantum states J′ = 0, 1, 2 of the inner well vibrations (υ′ ≤ 8) in the state of molecular hydrogen, were recorded in high resolution using a vacuum ultraviolet Fourier transform absorption spectrometer in the wavelength range 73–86 nm. Accurate line positions and predissociation widths are determined from a fit to the absorption spectra. Improved values for the line positions are obtained, while the predissociation widths agree well with previous investigations.Spectral lines, probing rotational quantum states J′ = 0, 1, 2 of the inner well vibrations (υ′ ≤ 8) in the state of molecular hydrogen, were recorded in high resolution using a vacuum ultraviolet Fourier transform absorption spectrometer in the wavelength range 73–86 nm. Accurate line positions and predissociation widths are determined from a fit to the absorption spectra. Improved values for the line positions are obtained, while the predissociation widths agree well with previous investigations.

Precision spectroscopy of high rotational states in H-2 investigated by Doppler-free two-photon laser spectroscopy in the EF (1)Sigma(+)(g)-X (1)Sigma(+)(g) system

Recently a high precision spectroscopic investigation of the EF1 Sigma(+)(g)-X-1 Sigma(+)(g) system of molecular hydrogen was reported yielding information on QED and relativistic effects in a sequence of rotational quantum states in the X-1 Sigma(+)(g) ground state of the H-2 molecule [Salumbides et al., Phys. Rev. Lett. 107, 043005 (2011)]. The present paper presents a more detailed description of the methods and results. Furthermore, the paper serves as a stepping stone towards a continuation of the previous study by extending the known level structure of the EF1 Sigma(+)(g) state to highly excited rovibrational levels through Doppler-free two-photon spectroscopy. Based on combination differences between vibrational levels in the ground state, and between three rotational branches (O, Q, and S branches) assignments of excited EF1 Sigma(+)(g) levels, involving high vibrational and rotational quantum numbers, can be unambiguously made. For the higher EF1 Sigma(+)(g) levels, where no combination differences are available, calculations were performed using the multichannel quantum defect method, for a broad class of vibrational and rotational levels up to J = 19. These predictions were used for assigning high-J EF levels and are found to be accurate within 5 cm(-1).

The D-1 Pi(u) state of HD and the mass scaling relation of its predissociation widths

Absorption spectra of HD have been recorded in the wavelength range of 75?90?nm at 100?K using the vacuum ultraviolet Fourier transform spectrometer at the Synchrotron SOLEIL. The present wavelength resolution represents an order of magnitude improvement over that of previous studies. We present a detailed study of the D1?u?X1?+g system observed up to v? = 18. The Q-branch transition probing levels of ?? symmetry are observed as narrow resonances limited by the Doppler width at 100?K. Line positions for these transitions are determined to an estimated absolute accuracy of 0.06?cm?1. Predissociation line widths of ?+ levels are extracted from the absorption spectra. A comparison with the recent results on a study of the D1?u state in H2 and D2 reveals that the predissociation widths scale as ??2J(J + 1), with ? being the reduced mass of the molecule and J the rotational angular momentum quantum number, as expected from an interaction with the B?1?+u continuum causing the predissociation.