Laser spectroscopic study of Mg atoms in pressurized liquid helium

Emission and excitation spectra of the 3s21S0-3s3p 1P1 transition of Mg atom in pressurized liquid helium-4 and helium-3 have been measured. In the emission spectra we have found that their transition wavelengths, which are significantly red shifted, remain constant or slightly increase with increasing the liquid helium pressure, whereas for other alkali-earth atoms the increase of the liquid pressure always shifts their emission spectra toward shorter wavelength. Our theoretical calculations based on a bubble model have successfully reproduced this unique spectral property, and have suggested the possibility of the formation of a Mg(3s3p 1P1)Hen exciplex in a bubble.