Time resolved measurements in high pressure mass spectrometry: An analysis of assumptions

Abstract

The assumptions underlying the use of time resolved measurements for the determination of ion–molecule reaction rate constants in high pressure chemical ionization sources have been examined and problems introduced by diffusion and drift are presented; these require conversion from ion currents to ion concentrations in the presence of applied fields when ion current ratios of different ions are used. Moreover, the existence of an irresolvable difference in the significance of arrival times of product and reactant ions is demonstrated, but it is shown how this error can be minimized. A method for the measurement of total disappearance rate constants for association reactions is demonstrated and applied to the reaction CO+2+2CO2→ (CO2)+2+CO2; the third order rate constant for this process is 1.5±0.1×10−28 cm6 sec−1 at 409° K.