Mladen Movre

Resonance interaction and self-broadening of alkali resonance lines. I. Adiabatic potential curves

Adiabatic potential curves were calculated using perturbation theory for the long-range electrostatic interaction between two alkali atoms of the same species, one being in the ground state, the other in the resonance-excited state. Comparison with recent experiments showed that the observed satellites and asymmetries in the self-broadened quasi-state wings of the alkali resonance lines are the consequence of extrema in certain potential curves between the fine-structure levels.

Cesium dimer spectroscopy on helium droplets

Visible absorption spectra of cesium-doped helium nanodroplets between 14,500 and 17,600 cm(-1) were probed by laser-induced fluorescence. A strong absorption band peaking around 16,700 cm(-1) is identified as Cs2 1(a) 3Sigmau+-3 3Sigmag+ transition. A broad unstructured band near 17,520 cm(-1) is assigned as the Cs2 1(X) 1Sigmag+-2 1Sigmau+ transition. Explanations of the observations are discussed on the basis of ab initio potential curves calculated by Spies and Meyer [(unpublished)]. All spectra have been modeled using narrow Frank-Condon windows around the equilibrium internuclear distance of the lowest singlet and triplet states. Many observed absorption peaks of smaller intensities could be identified, some of which may be due to transitions of cesium trimers formed on the droplets.

Resonance interaction and self-broadening of alkali resonance lines. II. Quasi-static wing profiles

For pt.I see ibid., vol.10, no.3, p.2631 (1977). Calculates the oscillator strengths from the ground level to the first excited states of the long-range alkali homonuclear dimers. Using the known resonance interaction potential curves and these oscillator strengths the authors calculated the quasi-static wing profiles of the self-broadened first resonance alkali lines.

Near-wing asymmetries of the self-broadened first Rb and Cs resonance lines

The authors have measured small asymmetries in the near wings of the self-broadened first resonance lines of Rb and Cs. The transitions from the impact to the quasi-static profile were observed. A comparison with recent calculations by Movre and Pichler (1975) reveals satisfactory agreement.

Predictions for the observation of KRb spectra under cold conditions

Quantum-mechanical simulations of the excitation spectra of KRb from the lowest vibrational level of the lowest triplet and singlet electronic states have been performed using recently calculated interaction potential curves and corresponding transition dipole moments. The obtained spectra can be used for a comparison with experimental absorption spectra of KRb molecules produced in their vibronic ground state or attached to cold helium droplets. In addition, we compare the semiclassically simulated spectra with absorption measurements in dense K–Rb vapour at high temperatures, which helped us to identify three diffuse bands as 1 3 � + –3 3 � ,1 3 � + –4 3 � and 1 1 � + –4 1 � + transitions. The first may be observable in an excitation spectrum of KRb dimer formed on cold helium droplets.

The non-Lorentzian wings of alkali resonance lines: the determination of the atom number density in pure and mixed alkali vapours

The improved method for the determination of the atom number densities in pure and mixed alkali vapours has been proposed. In order to obtain the correct results one has to go beyond the simple Lorentzian shape of the quasistatic absorption profile. The method has been tested by the white-light absorption measurements in the pure K, Rb and Cs vapours. The statistical accuracy of the obtained data for the atom number density is +or-3%. The method has been applied for determining the atom number densities in the vapour over the Rb-Cs mixture. The obtained values have been used in the evaluation of the effective C6 constants for Rb*-Cs interaction: C6eff=(4.9+or-0.3)* 10-30 cm6 s-1 for the D2 line. The theory predicts C6eff=4.95*10-30 cm6 s-1 for the D1 line and C6eff=2.37*10-30 cm6 s(-1) for the D2 line.

Optimization of lead metastable production in a low pressure argon discharge

Abstract The spatial distribution of 6p 2 3 P 1 and 6p 2 3 P 2 lead metastable atoms in a radially symmetric low pressure argon discharge has been investigated by absorption measurements. The number density of lead as well as the argon pressure were varied independently. The measurements performed to find optimum conditions for metastable production in the discharge also revealed the diffusion and the collisional depopulation of the metastable species in argon.

The collision cross sections for excitation energy transfer in Rb*(5P3/2) + K(4S1/2) → Rb(5S1/2) + K*(4P J ) processes

The collisional excitation transfer for the processes Rb*(5P3/2)+K(4S1/2) → Rb(5S1/2)+K*(4PJ),J=1/2, 3/2, was investigated using two-photon laser excitation technique with a thermionic heat-pipe diode as a detector. The population densities of the K 4PJ levels induced by collisions with excited Rb atoms as well as those produced by direct laser excitation of the potassium atoms were probed through the measurement of the thermionic signals generated due to the ionization of the potassium atoms emerging from the K(4PJ) → K(7S1/2) excitation channel. The measurements of the thermionic signals in addition to the spectroscopic determination of the potassium number density yield the following values for the excitation transfer cross sections: σ1(Rb 5P3/2 → K 4P1/2)=8 Å2 and σ2(Rb 5P3/2 → K 4P3/2)=11 Å2. The accuracy of the presented results is ∓15%. The obtained results are compared to those for the opposite processes K*(4PJ)+Rb(5S1/2) → K(4S1/2)+Rb*(5P3/2).

Caesium 6P fine-structure mixing and quenching induced by collisions with ground-state caesium atoms and molecules

Applying the cw laser fluorescence method, the cross sections for the fine structure mixing and quenching of the Cs 6P state, induced by collisions with ground-state caesium atoms and molecules, have been measured. Caesium atoms were optically excited to the 5DJ states via quadrupole-allowed 6S1/25DJ transitions, while the resonance states were populated by the radiative and collisional 5DJ6PJ transitions. The relative populations of the Cs 6PJ sublevels, as well as ratio of the 5D3/2 to 6P3/2 populations, were measured as a function of the caesium ground-state number density. From these measurements we obtained the cross section of (14±5) × 10-16 cm2 at T = 585 K for the process Cs(6P1/2)Cs(6P3/2) induced by collisions with ground-state caesium atoms. The applied experimental approach enabled the determination of the effective spontaneous rates for the 6PJ states which are in agreement with the predictions of Holsteins theory. The cross sections for quenching of 6PJ by caesium atoms and molecules were measured at T = 635 K and the obtained values are (1.6±1.4) × 10-16 cm2 and (1210±260) × 10-16 cm2, respectively. Using recently calculated Cs*+Cs potentials we performed an analysis which shows a good agreement between the measured values and the theoretical estimates.

The collision cross sections for the fine-structure mixing of caesium 6P levels induced by collisions with potassium atoms

The cross section for the fine-structure excitation transfer Cs(6P1/2) → Cs(6P3/2), induced by collisions with the ground state potassium atoms, has been measured by resonant Doppler-free two-photon spectroscopy. The population densities of caesium 6PJ (J=1/2, 3/2) levels were probed by thermionic detection of the collisionally ionized caesium atoms from the Cs(6PJ) → Cs(10S1/2) excitation channel. The cross section for the transfer process at the temperatureT=503 K has been found to be σ(1/2 → 3/2)=45 Å2 ± 20%. The result is compared with previously published experimental cross sections for fine-structure transfer in resonance states of other alkali elements perturbed by potassium and a thoeretical value of the Li(2PJ)-K system calculated in a simple approach.