Calculated pressure broadening and shift for alkali-metal atoms perturbed by rare gases: Two-photonS−Stransitions

The broadening and shift of two-photon $S-S$ transitions (e.g., in alkali-metal atoms perturbed by rare gases) are shown to be readily calculable. These calculations employ (a) newly available expressions for alkalimetal-rare-gas long-range potential coefficients $C_6$, $C_8$, and $C_{10}$; and (b) the (herein discussed) appropriate form of impact theory (particularly simple since only a single potential curve is involved and inelastic processes are not usually important). It is demonstrated in particular that the influence of $C_8$ and $C_{10}$ terms on the broadening and shift is significant though not dominant. Comparison with recent experimental data on the Na-rare-gas pairs shows reasonable agreement for the heavy rare gases.