Spectroscopic studies on Yb⁺ ions in liquid helium

An emission spectrum of the 4f¹⁴ 6s ²S_1/2-6p²P_1/2 (D1) transition and excitation spectra of the 4f¹⁴ 6s ²S_1/2-6p²P_J (J=1/2 (D1) and 3/2 (D2)) transitions of Yb⁺ ions in liquid helium have been observed by means of a laser-induced fluorescence method. It has been found that all these spectra are blue-shifted from the ones in the free space, and also that the D2 excitation spectrum has double peaks. To understand these spectra, theoretical calculations have also been carried out based on a vibrating bubble model, in which the bubble surface is assumed to vibrate in the spherical (breathing), dipolar and quadrupolar modes. As a result, it has been found that the blue shifts are well understood with this bubble model, and also that the dynamic Jahn-Teller effect due to the quadrupole vibration of the bubble plays an important role for the double-peaked profile of the D2 excitation spectrum.