The 3d←3p endothermic collisional population transfer of Li in He and Ar at 298 K

The 3p state of Li was excited in He and Ar buffer gases at room temperature (298 K) and the time profiles of sensitized fluorescence from the 3s and 3d states were measured. The 3d←3p endothermic population transfer rates determined from the pressure dependence of the time profiles were 6.5×10−11 cm3 s−1 for He and less than 10−3 cm3 s−1 for Ar. The origin of this large difference between He and Ar is discussed in terms of non-adiabatic transitions between the 3p and 3d molecular states of the Li–He and Li–Ar molecules.