Laser excited, state detected calcium-rare gas collisional energy transfer: Ca(4s5p 1P1) spin changing and Ca(4s5p 3P1) fine structure changing cross sections

Abstract

Pulsed dye laser excitation along with time and wavelength-resolved fluorescence detection techniques are used to measure cross sections for state changing collisions of Ca(4s5p 1P1) and Ca(4s5p 3P1) with the rare gases He, Ne, Ar, Kr, and Xe. The Ca(4s5p 1P1)+M deactivation involves a near-resonant spin changing process which populates predominantly the Ca(4s5p 3P2,1,0) states. The total deactivation cross sections for 1P1 are 22, 25, 5, 3, 13, and 31 Å2 (±20%) for 3He, 4He, Ne, Ar, Kr, and Xe, respectively. The cross sections for Ca(4s5p 3P1)+M fine-structure changes are 38, 25, 46, 56, and 135 Å2 (±35%) for He, Ne, Ar, Kr, and Xe, respectively. Branching ratios for the electronic energy transfer Ca(4s5p 1P1)+He⇄Ca(4s5p 3Pj, 3d4p 3Fj, and 3d4p 1D2)+He are determined to be 90±3:6±4:3±2, respectively, compared to statistical values of 26:60:14. The predominant product states 4s5p3P2,1,0 are produced by a near-resonant spin changing process; the fine structure components of the 3P state are populated essentially statistically (55:33:11). Fine-structure branching Ca(4s5p 3P1)+M⇄Ca(4s5p 3P2,0)+M is also measured and gives a statistical distribution of Ca(4s5p 3P2,0) states. The radiative lifetimes of the 4s5p 1P1 and 4s5p 3P1 levels are measured to be 65±2 and 71±8 ns, respectively. The results are discussed in terms of the competing effects of velocity and interaction strengths on the curve crossing probabilities.