Assuming thermal equilibrium is fully achieved, at 1,000 K, the ion yields estimated according to equations ( ) and ( ) are 10 -8 and 10 -7 , respectively. These numbers are significantly lower than experimental values (~10 -4 ). At 2,200 K, the estimated ion yields are 10 -4 in both cases. The number is consistent with experimental values. As discussed earlier, the plume temperature may be lower than 2,200 K, and thus, the estimated ion yields may be lower than the observed numbers and ions directly from the solid sample may be needed to justify a portion of the observed ion yields.