Hyperfine interactions in homonuclear diatomic molecules and u-g perturbations. I. Theory

The hyperfine interactions in heavy homonuclear diatomic molecules are studied theoretically. The general matrix element of the related Hamiltonian is derived in the general case and detailed in the case of an ensemble of electronic states sharing the same dissociation limit. The predicted hyperfine perturbation effects are illustrated through the example of the iodine B state. In particular a mixing of the B 0+u state with a 1g state is to be expected near the dissociation limit. As the calculation methods apply to any non-zero nuclear spin homonuclear diatomic molecule, similar u-g symmetry breakings are likely to be met in other molecules.Les interactions hyperfines dans les molécules diatomiques homonucléaires lourdes sont étudiées théoriquement. L'élément de matrice du Hamiltonien est établi dans le cas général et explicité dans le cas d'un ensemble d'états électroniques ayant une limite de dissociation commune. Les effets de perturbation hyperfine en résultant sont illustrés dans l'exemple de l'état B de l'iode. En particulier, un mélange de l'état B 0+u avec un état 1g est prévu près de la limite de dissociation. Comme les méthodes de calcul s'appliquent à toute molécule diatomique homonucléaire ayant un spin nucléaire non nul, on peut s'attendre à rencontrer de similaires brisures de symétrie u-g dans d'autres molécules

Utilisation d'une expérience de résonance électrique. Radiofréquence sur des niveaux excités dans un faisceau d'ions accélérés à la détermination des sections efficaces d'excitation. Application au niveau n = 6 de 4He+

The optical détection of an electric resonance between hydrogenoid levels on beamfoil excited ions, can be applied to the determination of excitation cross-sections. We study the possibilities of this method by referring to an experience on the n = 6 4He+ level. Since the signals from various ML sub-levels are correlated the method allows only the determination of a few linear combinations of excitation cross-sections.La méthode de détection optique d'une résonance électrique entre niveaux hydrogénoïdes sur un faisceau d'ions excités par cible solide mince peut être utilisée pour déterminer des sections efficaces d'excitation. Nous étudions, en nous référant à une expérience faite dans le niveau n = 6 de 4He+, les possibilités de la méthode. Nous en concluons que, compte tenu des corrélations entre signaux des sous-niveaux ML, on ne peut atteindre que certaines combinaisons linéaires des sections efficaces d'excitation

ELECTRONIC ENERGY TRANSFER IN THE LOW - LYING CHARGE TRANSFER STATES OF I2I_{2}

The D'2g-A'2u transition in $I_{2} (340 nm I_{2} UV Laser)$ was excited using two CW lasers. A rotational analysis of this system was performed. The observation of high vibrational levels of the A'2u state permitted a long range analysis of this state resulting in absolute energies of D'2g and A'2u relative to $X^{1}{\Sigma_{y}}^{+} (\upsilon = 0 - J = 0)$. In order to study the collisional energy transfer among the low-lying charge transfer states of $I_{2}$ responsible for the observation of the D'2g - A'2u transition, we excited specific $E {O_{g}}^{+}$ rovibronic levels to study transfer to $D {O_{u}}^{+}$ and D'2g levels. The various mechanisms will be discussed

THE ATOMIC ORIGIN OF THE ELECTRONIC MOLECULAR STATES FROM THEIR HYPERFINE STRUCTURE

International audienceWhen the internuclear distance in a diatomic molecule is sufficiently large that the exchange interactions are negligible, a good representation of the molecular wavefunctions may be obtained from a separated-atom basis set. In this representation the molecular hyperfine interactions can be predicted from their related atomic values. As examples we have solved completely the calculations for the hyperfine structure for two iodine molecular states, namely the X(1Σ+g) and the E(O+g) states. The results are in good agreement with experimental determinations. The E(O+g) state is a ion-pair state and our predictions when compared with the experimental values clearly descriminate the atomic origin between the different possible asymptotes

Hyperfine interactions in homonuclear diatomic molecules and u-g perturbations. II. Experiments on I2

The iodine B 0+u state is studied near its dissociation limit using sub-Doppler high resolution techniques. The recording of more than 10 000 hyperfine lines allows a systematic analysis of the hyperfine structure. All the observed features can be accounted for by the calculation of the interactions of the B state with the other electronic states sharing the same dissociation limit. Three different situations are encountered : weak perturbation situations treated in the second-order approximation of the Broyer, Vigué, Lehmann theory, superhyperfine structures observed in several band heads, and strong perturbation cases (vibrational levels ν' = 76, 77 and 78). This last situation has required the utilization of the full exact interaction matrix of B 0+u with a 1 g state, leading to the first direct evidence of a u-g symmetry breaking in a homonuclear diatomic molecule.L'etat B 0+u de l'iode est étudié près de sa limite de dissociation par une technique sub-Doppler haute résolution. L'enregistrement de plus de 10 000 raies hyperfines permet une étude systématique de la structure hyperfine. Toutes les observations peuvent être interprétées à partir du calcul des interactions hyperfines dues aux autres états électroniques ayant la même limite de dissociation. Trois situations différentes sont rencontrées: les perturbations faibles traitées dans la théorie de Broyer, Vigué et Lehmann de l' approximation du second ordre, les structures superhyperfines observées dans plusieurs têtes de bande et le cas des perturbations fortes (ν' = 76, 77 et 78 ) . Cette dernière situation a demandé l'utilisation de la matrice complète d'interaction de l'état B 0+u avec un état 1 g, conduisant à la première mise en évidence d'une brisure de symétrie u-g dans une molécule diatomique homonucléaire

Hyperfine Structure of Rovibrational Levels Near the Dissociation Limit of the Iodine B State Excited by the 5017 Å Ar+ Laser Line

International audienc

INTRACAVITY LASER INDUCED FLUORESCENCE RESOLVED BY FT SPECTROMETRY

Author Institution: Laboratoire de Spectrom\'{e}trie Ionique et Mol\'{e}culaire (UMR 5579 CNRS), B\^{a}timent A. Kastler, Universit\'{e} Lyon I, Domaine Scientifique de la DouaResolved fluorescence spectra produced with intracavity excitation show that the combination of Fourier transform and intracavity FT/LIF techniques (ICLIF) holds great promise for observing weak electronic transitions. We give here preliminary results on alkali dimers $(K_{2})$, illustrating the potentiality and the limitations of this combination for electronic spectroscopy. It is shown that interaction volumes between the molecular source and the laser beam (diameter 0.4 mm) are increased by a factor of 25 using a single mode Spectra Physics 380 ring cavity, rebuilt in our laboratory for the purpose. Two-photon processes are clearly enhanced in high resolution FT Spectra, and collisional features and transitions to rovibrational levels close to the ground state dissociation limit have been observed. ICLIF is adapted to the study of weakly absorbing systems. It allows access to gerade levels for species with a centre of inversion, which are not probed directly by one-photon absorption methods (including CRDS)

Hyperfine structure of higher rovibrational levels in the iodine B state studied by Ar+ laser induced fluorescence

International audienceThe hyperfine structure of higher rovibrational levels in the iodine B state has been investigated by studying the fluor-escence of a well collimated iodine molecular beam excited by the 5017A AI+ laser line. Nine transitions: R(13) 61-0, P(12)61-0, R(49) 67-0, R(39)64-0, R(26)62-0, P(56)73-0, R(54)70-0, R(55)77-1, R(51)6W were identified and their center of gravity located to an accuracy of kO.001 cm-'. A fit of the theoretically predicted hyperfine patterns to the ob-served spectra enables one to study the variation of the magnetic hyperfine constant C' with the vibrational quantum num-ber U' in the range 61 Q U' < 73. The observed behavior is well accounted for by a simple theoretical model developed by Vigu6 et al