VUV spectroscopic study of the D1Piu state of molecular deuterium

The D^1\Pi_u - X^1\Sigma_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 \Pi^- symmetry, were observed up to vibrational level v = 22. The states of \Pi^+ 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 \Pi^- 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.Comment: 16 pages, 10 figures, 2 tables, supplemental material with an additional tabl

DOUBLY EXCITED STATES OF H2H_{2}.

Author Institution: Laboratoire de Spectroscopie Hertzienne de l'ENS - Universit\'{e}Neutral double excited states of $H_{2}$ lie in the Franck Condon region, at energies beyond 23 eV above the ground state of $H_{2}$, far above the ionization threshold. Dissociation into neutral fragments does complete with autoionization. The dissociation limit of such doubly excited states is not as simple as it first appears. For instance the states with $(2p\sigma_{u},n\ell\lambda_{u})$ configuration at short internuclear distance, are correlated to $H(1S) + H^{+} (n'\ell)$ or to $H^{+} + H^{+} (1s, n\ell)$; which limit is important? To reach such $H(1S) + H^{+} (n^{\prime}\ell^{\prime})$ limit the corresponding potential curve has to cross all the potential curves of bound states with $n^{\prime\prime}n^{\prime}$ are these crossings efficient? We will discuss how a quantitative study of the photodissociation of these states gives some enlightenment on the problem

Two-step excitation of molecular hydrogen

A stepwise excitation of H2 is performed. Electron impact populates the metastable c 3Π u state then an optical resonance allows the excitation of 3Σg, 3Πg or 3Δg states. We observed the selectivity of the electron impact excitation. The laser light used for the optical resonance was linearly polarized, the alignment produced allowed the observation of the Hanle effect on the 3 dδ 3Δg, v = 2, K = 2, I = 1 level.Des molécules d'hydrogène excitées par impact électronique dans l'état métastable c 3Π u sont portées par résonance optique dans un état 3Σ g, 3Πg ou 3Δ g. La sélectivité de l'excitation électronique est mise en évidence. La lumière du laser utilisée pour la seconde excitation est polarisée linéairement ; l'alignement ainsi produit a permis d'observer l'effet Hanle du niveau 3 dδ3Δ g, v = 2, K = 2, I = 1

On the orientation of molecular photofragments produced in highly excited rotational states

The degree of orientation of highly excited rotational states of molecular fragments produced by photodissociation with circularly polarized light is studied quantum mechanically. It is shown that a significant orientation of the fragments' angular momentum j can be obtained when two or more dissociative continua correlated to the same final state of the products are excited simultaneously. In addition, the coherently excited continua should correspond to different helicity states, that is, to different projections of j on the reaction coordinate R (the vector joining the centers of mass of the fragments). The particular cases of an initial total angular momentum equal to zero as well as the axial recoil limit are discussed. The theory is applied to a simplified model of the photodissociation of ICN in the A continuum. The calculations have been performed by integration of the time independent quantum close-coupling equations for the coupling between the rotation of CN and the reaction coordinate R, using recently proposed potential energy surfaces and couplings. The results reproduce qualitatively the experimental results of Hasselbrink, Waldeck, and Zare [Chem. Phys. 126, 191 ( 1988)], in particular, the change of sign and the large degree of orientation found for highly excited rotational states of the CN fragments. © 1992 American Institute of Physics.The calculations presented here were carried out on the VP200 computer at CIRCE (Orsay).Peer Reviewe

Direct optical access to the triplet manifold of states in H 2

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Vibrational predissociation of the 4pσ B ″ levels of D 2 : an anomalous isotope effect

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