Threshold ionization and dissociation of t-butylamine

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 ?fH₂₉₈ for (CH3)2CNH2 + of 603 ± 3 kJ mol^-1. This value is ~10 kJ mol^-1 higher 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 ?fH₂₉₈ leads to a ?fH₂₉₈ for 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 + ?fH₂₉₈) 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.