Intralines of Quasi-Conical Intersections on Torsion Planes: Methylamine as a Case Study

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2009-06, Vol.113 (24), p.6756-6762
• Main Authors: Levi, C, Halász, G. J, Vibók, Á, Bar, I, Zeiri, Y, Kosloff, R, Baer, M
• Format: Article
• Language: English
• Subjects: A: Molecular Structure, Quantum Chemistry, General Theory; Methylamines - chemistry; Models, Chemical; Quantum Theory
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp901072u

Recently we reported on a novel feature associated with the intersection of the two lowest states 1A′ and 1A′′ of the methylamine (J. Chem. Phys. 2008, 128, 244302). We established the existence of a finite (closed) line of conical intersections (ci), namely, a finite seam, located in the HC−NHH symmetry plane, a line that is formed by moving a single hydrogen on that plane while locking the positions of the (six) other atoms. In the present article, this study is extended to the corresponding torsion planes formed by rotating the methyl group around the CN axis. The torsion planes, in contrast with the HC−NHH symmetry plane, do not satisfy the symmetry feature that enables the seam just mentioned. Nevertheless, the calculated nonadiabatic coupling terms (NACTs) resemble features similar to those encountered in the HC−NHH symmetry plane. Following a tedious numerical study supported by a theoretical model (Section ), it was verified that these NACTs may become similar to those on the symmetry plane, sometimes even to the level of almost no distinction, but lack one basic feature; namely, they are not singular and therefore do not form topological effects.