High resolution electronic spectroscopy of p-toluidine. A precessing rotor model for G12 molecules

Abstract

High resolution core-level electron spectroscopy on free molecules and atoms AIP Conf.Based on a study of the high resolution SIr-SO fluorescence excitation spectrum of p-toluidine (p-methylaniline) and related G 12 molecules, we propose that the threefold axis of the methyl group is tilted slightly with respect to the symmetry axis of the molecular frame, and exhibits a kind of precessional motion in the course of its hindered internal rotation. We derive a new Hamiltonian to describe this motion and show that it is consistent with previous modifications of the traditional torsion-rotation Hamiltonian first proposed by Wilson, Lin, and Lide [J. Chem. Phys. 23, 136 (1955)]. Applying the new Hamiltonian to the SIr-SO spectrum of p-toluidine, we have determined the sixfold barrier heights V 6 (So) = ( -) 5.6 and V 6 (Sl) = ( -) 43.9 cm-I, values that are similar to those of toluene and other 4-substituted toluenes.

High Resolution Electronic Spectroscopy of o- and m-Toluidine in the Gas Phase. Barrier Height Determinations for the Methyl Group Torsional Motions

“…Figure 1 shows the vibrationally resolved fluorescence excitation spectra of o-toluidine and m-toluidine obtained by Ito and co-workers. 5 In this figure, a labeling scheme of the vibrational bands 0a 1 , 1e, 2e, and so forth is used where a number indexes the upper state torsional levels and a letter designates their symmetries. In the infinite barrier limit, the levels 0a 1 and 1e, 2e and 3a 1 , and so forth are degenerate.…”

S0 and S1 spectroscopy of jet cooled 9-cyano-10-methylanthracene: The methyl group as a molecular rotor

“…Extensive studies of the toluene derivatives [7][8][9], methylnaphthalenes [10], methylanthracenes [11,12] as well as methylbenzyl radicals [13], illustrate that the internal rotation barriers strongly depend on the position of the CH 3 group in the molecule and on particular vibronic excitation. In effect, the ground state barrier extends over a relatively wide region, from $5 cm À1 for toluene [8] up to 800 cm À1 in 1-methyl-naphthalene [10].…”

A General Rotation–Contortion Hamiltonian with Structure Relaxation: Application to the Precessing Internal Rotor Model

“…the function P(t), E is an eigenvalue, and G(t, E) is a function of t and of E. We use the recursion formula II. 1…”

“…[2] to [4] Ĵ x , Ĵ y , and Ĵ z are the components of the on the program), although the level of convergence achieved with a given size of basis set will change. total angular momentum operator along molecule fixed axes, Ĵ t Å 0iបÌ/Ìt is the torsional angular momentum operator, m is the determinant of the 4 1 …”

“…This Hamiltonian de-Hamiltonian of Ref. (1) and find that the error in the latter scribes the methyl internal rotor as rigidly rotating about a is significant for large values of the tilt angle. tilted and precessing internal rotation axis, where the axis of internal rotation precesses at three times the rate of the…”