Y. Le Duff

Raman scattering of HF in the gas state and in liquid solution

We have studied the Raman scattering of HF in the gas state and dissolved at low concentration in liquid SF6. For the gas, the absolute intensity of the vibrational band has been measured and the polarizability derivative has been determined to be d α/d r = 1.00 × 10−16 cm2. The system HF perturbed by 23 atm of gaseous SF6 is discussed; we also give some results on the HF polymer bands at 2900–3800 cm−1.

Multiphoton rotational line strength in diatomic molecules between two Hund's case (a) states

The n-photon rotational line strength (RLS) in diatomic molecules is studied for transitions between two states which both belong to Hunds case (a). The expression of the n-photon RLS is given for n identical photons linearly polarized and n identical photons circularly polarized, in the Born-Oppenheimer approximation and neglecting rotational contributions to the energies of the intermediate states. The selection rules are also given.

Raman band shape of the N2 molecule dissolved in liquids

We have studied the vibrational Raman band of the N2 molecule dissolved in various solvents. The band shape of isotropic and anisotropic scattering is discussed and compared with the one obtained from N2 gas. A collisional narrowing effect has been observed for the isotropic scattering. For N2 dissolved in SF6 the rotational correlation function is analyzed.

J Dependence of the depolarization ratio of the rotational components of the Q branch of the H2 and D2 Raman band

The theory on rotational structure of Raman bands predicts‐apart from the (2J+1) magnetic degeneracy‐an additional J dependence of anisotropic scattering. This implies a J dependence of the depolarization ratio, when measured for the separated rotational components J → J of the Q branch of Raman bands. We report here on experimental results obtained on the transitions J=0, 1, ···, 4 of the Q branch of H2 and D2, which are in full agreement with theory. In particular we demonstrate the completely isotropic character of the O–O transition. Our experimental value for the depolarization ratio of the total vibrational Raman band of H2 agrees well with the one obtained recently by ab initio calculations.

Collision-induced scattering for molecules

The object of this investigation was to study experimentally the depolarized integrated Rayleigh intensity induced by collision of optically isotropic molecules CF4, CH4, SF6 at densities up to 350 amagats. We have compared the results at low densities with the pair approximation dipole-induced dipole theory. We have found that at high densities this intensity measured relatively to a Raman vibration line is maximum at a density lower than the critical density.

Raman band shapes of small diatomic molecules dissolved in inert liquids

Abstract The experimental results obtained on four different types of Raman spectra: pure rotational lines, the IVV and VH components of the vibrational Q-branch and the vibrational rotational lines are presented for H2, D2, HF and N2 dissolved at low concentration in inert solvents. The line broadening and motional narrowing due to the solvent interaction is discussed.

Multiphoton rotational line strengths in diatomic molecules for intermediate Hund's (a-b) coupling case

Rotational line strength expressions are derived for n-photon transitions between two multiplet states of diatomic molecules which both belong to coupling cases that are intermediate between Hunds case (a) and case (b). Rotational selection rules for n-photon transitions are given. For doublet states, rotational line strengths are given in terms of coupling parameters, states with any multiplicity may be treated in the same way. Different kinds of transitions are discussed.

Line shape of the collision-induced scattering in CF4

Results on the spectral shape of the collision-induced scattering (CIS) of CF4 gas are obtained for densities up to 270 amagats (296 K). For low frequencies they are compared with dipole-induced dipole theory; for high frequencies a short distance-induced binary collision model describes the observed spectral shape fairly well.

Intensity enhancement of the NO C 2Π(v = 0) fluorescence in the presence of rare gases

Fluorescence of the predissocd. C2P(v = 0) state of NO in the presence of rare gases was investigated by using selective excitation with synchrotron radiation. In the presence of Ar an anomalous pressure behavior was obsd.: at low pressures (0-30 torr), the fluorescence intensity was quenched, but at higher pressures (30-400 torr) an enhancement of intensity was obsd. Furthermore the C(0)-A(3) cascade was induced. Similar results are reported for the other rare gases except for Xe, for which only quenching was obsd. It is suggested that the intensity enhancement is due to a decrease in the no. of mols. undergoing dissocn. [on SciFinder (R)]

Pressure effects in multiple resonant multiphoton transitions

Abstract Although the rotational structure of a multiphoton process generally remains unaltered over a large range of gas pressure, this is not the case when multiple resonances are present. The rotational structure observed through intermediate rotational levels in a multiphoton process depends strongly on the resonance conditions. We show, for the NO molecule, that this structure changes drastically when the resonance conditions are modified by intermolecular collisions.