An intraline of conical intersections for methylamine

Abstract

In this article are considered the conical intersections ͑ci's͒ related to the N-H bond in the methylamine, CH 3 NH 2 , molecule. The novel feature that was revealed is that the two lowest states 1AЈ and 1AЉ are coupled by a line of cis located in HC-NHH plane-a line that is formed by moving a single hydrogen on that plane while fixing the ͑six͒ other atoms. The validity of this line was proven first by studying the singularities of the ͑angular͒ nonadiabatic coupling terms and then by revealing the degeneracy points formed by the two interacting adiabatic potential energy surfaces ͑PESs͒. A theoretical analysis indicated that the line has to be a finite closed line. We also calculated the Berry phase for a contour that surrounds this line and found it to be 3.127 rad, namely, a value reasonably close to . The existence of such lines of cis-instead of isolated cis ͑as exhibited by other n-atomic ͑n Ͼ 3͒ molecules such as HNCO or C 2 H 2 ͒-may enhance significantly the transition rate from an upper adiabatic state to a lower one. There are also numerical advantages in such situations, that is, if such a line is properly placed in that plane ͑like in the present case͒ the wave-packet treatment of the nuclei can be carried out employing a single diabatic PES instead of having to consider two coupled PESs.

Formation of Vibrationally Excited Methyl Radicals Following State-Specific Excitation of Methylamine

“…The photochemistry of methylamine after excitation in its first UV absorption band has been the subject of significant experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretical [18][19][20][21][22][23][24] attention. Methylamine is the simplest alkyl-substituted analog of ammonia, which provides an almost textbook example of the influence of exit-channel conical intersections on photodissociation dynamics.…”

“…This conical intersection has been the subject of particular theoretical interest recently, and as we argue below, provides an important means of internal conversion, transferring population from S1 to S0. 20,21,23 For convenience in the following, we indicate all electronically excited products with an asterisk.…”

A novel intraline of conical intersections for methylamine: A theoretical study

“…This line, presented in Ref. [18], was found to nearly overlap with the seam (the deviations were within the error-limit of the calculations).…”

“…This just described line can be interpreted as a seam (defined as the continuous line that connects all these infinite number of ci-points) but is characterized by additional features. Evidences were given for the fact that this line is finite (all seams encountered, so far, are infinite) and most likely a closed line [18].…”

“…Our approach, which is based on ab initio treatments [1, 4 -6], was recently extended to larger systems and among them we performed a detailed study of the methylamine molecule, CH 3 NH 2 , consisting of seven atoms [18]. The structure of the molecule is given in Figure 1 where it can be seen that the methyl group, CH 3 , is separated from the amine group, NH 2 by the CN bond.…”