Triplet State Excitation of Alkali Molecules on Helium Droplets:  Experiments and Theory

Abstract

In this paper, we discuss the electronic structure of alkali dimer molecules in 3Pig states on the surface of a helium droplet. The perturbation due to the droplet will in general not satisfy rotational symmetry around the internuclear axis of the diatom and thus, in addition to a broadening and blue shift, will cause a splitting of electronic levels that are degenerate in the free molecules. We propose a model based on general symmetry arguments and on a small number of physically reasonable parameters. We demonstrate that such a model accounts for the essential features of laser-induced fluorescence (LIF) and magnetic circular dichroism (MCD) spectra of the (1)3Pig-a3Sigma+ transition of Rb2 and K2. Furthermore the MCD spectra, analyzed according to the approach of Langford and Williamson [J. Phys. Chem. A 1998, 102, 2415], allow a determination of the populations of Zeeman sublevels in the ground state and thus a measurement of the surface temperature of the droplet. The latter agrees with the accepted temperature, 0.37 K, measured in the interior of a droplet.

Electronically excited rubidium atom in a helium cluster or film

“…We are investigating Rb ‫ء‬ He n in the 1 2 ⌸ 3/2 state, where the formation of Rb ‫ء‬ He exciplexes has been observed, 7 as well as Rb 2 dimers in the triplet state, as studied experimentally in Ref. 60. We note that QMC is an equilibrium method, and the study of the dynamics of excitations of atom in a superfluid or solid 4 He matrix is a great theoretical challenge.…”

Molecular Beam Magnetic Resonance in Doped Helium Nanodroplets. A Setup for Optically Detected ESR/NMR in the Presence of Unresolved Zeeman Splittings

“…The scheme is the same as that presented in ref 42. For LIF spectra, the droplet beam is chopped in the pickup chamber at 19.4 Hz, and each channel of the counter is synchronously gated for exactly 20 ms.…”

“…In He nanodroplets, we have already exploited magnetic circular dichroism (MCD) to determine the electron spin temperature of alkali metal atoms and dimers 41,42 and to discriminate between spin-orbit splitting and Jahn-Teller distortion in trimers. 43 Here, we take it one step further and exploit it to implement ODMR in helium droplets.…”

Homo- and heteronuclear alkali metal trimers formed on helium nanodroplets. Part II. Femtosecond spectroscopy and spectra assignments

“…On the other hand, valuable information about the interaction of the dopant with the droplet may be obtained from helium perturbations. [23][24][25][26][27][28] Significantly improved spectral resolution can be achieved by time-domain spectroscopy using the femtosecond pump-probe technique 20,22 or by measuring fine and hyperfine structure directly in the microwave regime 29 . In previous experiments, high-spin alkali trimers formed on helium nanodroplets have been interrogated using laser spectroscopy 8,30,31 as well as sophisticated variations thereof in order to separate spectrally overlapping bands of various trimer a Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany.…”