Assuming thermal equilibrium is fully achieved in the plume, the interion distance in the ion pair is 1 nm, the temperature is 1,000 K, the sample composition is 10 pmol analyte in 25 nmol matrix, and plume pressure at the time thermal equilibrium is achieved and ratios of species in the plume are maintained until ion extraction is 10 atm, the estimated ion yield is 5.1 × 10 -3 , which is close to but somewhat higher than the experimentally determined value 10 -4 . If 0.5 nm is taken as the interion distance and the pressure is 10 atm, the estimated ion yield is 1.6 × 10 -6 .