In the gas phase, the tendency for neutralization via ion pair formation in equations (10-11) should be similar as discussed earlier. The tendency for neutralization via proton transfer as shown in equations (10-11) can be estimated using the corresponding equilibrium constants, and they are 334 kJ/mol or 10 17 and 490 kJ/mol or 10 , respectively when a pKa of 860 kJ/mol for the protonated N-7 of guanine, is used for Nuc-NH + , pKa of 1194 kJ/mol of sulfuric acid is used for HX, pKa of 1350 kJ/mol of carboxylic acid is used for M, and the plume temperature is assumed to be 1,000 K. At 2,200 K, the numbers become 329 kJ/mol or 10 8 for the case of equation (10), and 490 kJ/mol or 10 12 for the case of equation (11). In all the cases, the equilibria strongly favor the neutral species.