Spectroscopy of quasimolecular optical transitions: Ca(4s2 1S0↔4s4p 1P,4s3d 1D2)-He. The influence of radiation width

Abstract

We perform calculations using the semiclassical Fourier approach forquasimolecular spectrainduced by thermal collisions of the excited calcium atom (Ca*)with the helium atom in the groundstate (He) for the following quasimolecular optical transitions: (Ω = 0+,4s4p 1P)↔(Ω = 0+,4s2 1S0) and (Ω = 0+,4s3d 1D)↔(Ω = 0+,4s2 1S0) in the Ca-He quasimolecule. As a comparisonwiththe experimental results obtained under gas-cell conditions, weaverage the spectra understudy over the impact parameters and the Maxwellian distribution ofthe colliding particles. For theasymptotically forbidden Ca(4s2 1S0→4s3d 1D2)-He quasimolecular transition, the firstcomparison between the calculated spectral line profile and theexperimental one is made not only inshape, but also in absolute value. We clarify the physical mechanismsfor the initiation ofa spectral line satellite at the position of the forbidden atomictransition being investigated. Thereasonable agreement confirms that the spectral lineshapes of theasymptotically forbiddentransitions are formed due to the interplay between the structure ofthe potential energy curvesinvolved and the strong dependence of the radiative width.