On the electronic states and photochemistry of simple alkyl amines

Abstract

This paper extends recent work on the excited states of methyl amine to some other simple amines. Jet-cooled mass-resolved multiphoton ionization spectroscopy is reported for methyl amine, dimethyl amine, trimethyl amine, ethyl amine, diethyl amine, and triethyl amine. A set of high-level calculations for methyl amine supports the assignment of S1 as a 3s Rydberg state by predicting the experimental transition energy to within about 1000 cm−1 after including vibrational zero-point energies for each potential energy surface. Perturbations observed in the experimental S1←S0 spectrum prompt a series of calculations which implicate a dissociative 3s Rydberg state in both the perturbation in the spectrum and in the photodissociation of methyl amine at these energies. A series of excited state calculations performed at the ground state geometry for methyl amine, dimethyl amine and trimethyl amine indicates the relative energies of the bound 3s and 3p Rydberg states as well as the first dissociative 3s Rydberg state. Taken together, this work presents a picture of the S1 and S2 excited states in which dissociative low-lying Rydberg states play a significant role in both the spectroscopy and photochemistry of the simple amines.