DIRECT DETERMINATION OF THE ADIABATIC IONIZATION-ENERGY OF NO2 AS MEASURED BY GUIDED ION-BEAM MASS-SPECTROMETRY

The adiabatic ionization energy (IE) of NO2 is measured to be 9.60 +/- 0.03 eV by studying the charge-transfer reactions of Zn+ , NO+ , and CH3I + with NO2 and those of NO2+ with alpha,alpha,alpha-trifluorotoluene and CH3I using guided ion-beam mass spectrometry. This value confirms the accuracy of a very precise spectroscopic value measured by Haber et al. [J. Chem. Phys. 144, 58 (1988) ] and Tanaka and Jursa [J. Chem. Phys. 36, 2493 (1962) ], IE(NO2) = 9.586 +/- 0.002 eV, but is much lower than many other measurements that are limited by very unfavorable Franck-Condon factors. The mechanism that allows the charge-transfer reactions to occur at the thermodynamic limit is discussed by examining qualitative potential-energy surfaces for the charge-transfer processes.