Threshold ionization and dissociation oft-butylamine

Abstract

The threshold photoelectron spectrum of t-butylamine, recorded between 8 and 28 eV, is reported for the first time. The spectrum was compared to orbital ionization energies calculated at the OVGF/cc-pVTZ level of theory. The adiabatic and vertical ionization energies of the outermost orbital (made up primarily of the nitrogen p orbital) are 8.48 ± 0.02 and 9.40 ± 0.02 eV, respectively. Threshold photoelectron photoion coincidence spectra were recorded between 8.5 and 35 eV, and appearance energies for 15 fragment ions were obtained. The lowest energy dissociation is the loss of a methyl group to form the (CH3)2CNH2+ion. RRKM fitting of this dissociation leads to a ΔfH298for (CH3)2CNH2+of 603 ± 3 kJ mol–1. This value is ~10 kJ mol–1higher than the previously derived value of Lossing et al. (based on an electron ionization appearance energy value) and the G3B3 estimate. Together with the proton affinity value of 932.3 kJ mol–1, the present ΔfH298leads to a ΔfH298for 2-propanimine (CH3)2C=NH of 5.3 kJ mol–1, which can be compared to a value of –5.7 kJ mol–1(based on the Lossing et al. (CH3)2CNH2+ΔfH298) and a G3B3 value of –0.3 kJ mol–1. At photon energies above 26 eV, there is evidence for the dissociative double ionization of t-butylamine forming either the singlet or triplet state of the dication.