Excimers in the Lowest Rotational Quantum State in Liquid Helium.

Authors :: Mendoza-Luna LG
Shiltagh NM
Watkins MJ
Bonifaci N
Aitken F
von Haeften K
Source :: The journal of physical chemistry letters [J Phys Chem Lett] 2016 Nov 17; Vol. 7 (22), pp. 4666-4670. Date of Electronic Publication: 2016 Nov 07.
Publication Year :: 2016
Abstract: Evidence for helium excimers (He <subscript>2</subscript> <superscript>*</superscript> ) in the lowest allowed rotational quantum state in liquid helium is presented. He <subscript>2</subscript> <superscript>*</superscript> was generated by a corona discharge in the gas and normal liquid phases. Fluorescence spectra recorded in the visible region between 3.8 and 5.0 K and 0.2 and 5.6 bar showed the rotationally resolved d <superscript>3</superscript> Σ <subscript>u</subscript> <superscript>+</superscript> → b <superscript>3</superscript> Π <subscript>g</subscript> transition of He <subscript>2</subscript> <superscript>*</superscript> . Analysis of the pressure and temperature dependence of lineshifts and line intensities showed features of solvated He <subscript>2</subscript> <superscript>*</superscript> superimposed on its gas-phase spectrum and, in the liquid phase only, pressure-induced rotational cooling. These findings suggest that He <subscript>2</subscript> <superscript>*</superscript> can be used to investigate bulk helium in different phases at the nanoscale.