Calculated and measured double-ionization energies to triplet electronic states of the doubly charged ions of methylamine, dimethylamine and trimethylamine

Double ionization of methylamine, dimethylamine and trimethylamine was studied experimentally by double-charge-transfer spectroscopy and theoretically both using an ab initio method with different basis sets and by the application of a semi-empirical form of the multiple scattering X alpha (MSX alpha) method. The use of OH+ and F+ projectile ions in the experimental work ensured that dications in triplet electronic states were produced. Also, the high velocity of the projectile ions ensured that vertical transitions from the molecules to the dications took place. Ab initio calculations predict quite well the observed reduction in the lowest double-ionization energies as the methyl content of the amine molecule increases. Application of the MSX alpha method allowed double-ionization energies to higher-lying tripler states of the dications to be predicted, providing a valuable insight into the electronic transitions which give rise to the spectra recorded for the three amines.