Torsions of N-methylpyrrole and its cation

Electronic, vibrational, and torsional couplings in N-methylpyrrole: Ground, first excited, and cation states

“…The REMPI/ZEKE 26 and 2D-LIF 27 apparatuses are the same as those employed earlier and in the recent study addressing the torsional levels in NMP and NMP + . 20 In all of the present experiments, a free-jet expansion of the vapor above room-temperature NMP liquid (Sigma-Aldrich, 99% purity) seeded in 2 bars Ar was employed.…”

“…Except where explicitly noted, vibrational transitions implicitly include transitions arising from both of the associated m = 0 and m = 1 levels, which will be almost perfectly overlapped in our spectra, as effective torsional rotational constants are very similar in the S 0 , S 1 , and D 0 + electronic states. 20 Torsional levels with |m| = 3n are non-degenerate, forming linear combinations for n ≠ 0. The splitting of the |m| = 3n (n ≠ 0) levels occurs as a result of the hindered rotation and, in a G 12 symmetry molecule, is characterized by the parameter V 6 .…”

“…NMP has a staggered orientation in its ground electronic state but an eclipsed orientation in the S 1 state and the ground state cation. 20,33…”

“…11 A theoretical study of the torsional levels in NMP was published by Kanamaru, 19 although we have questioned some of the conclusions of that work. 20 The low-lying electronic states of pyrrole and NMP are interesting, with occupied orbitals that are mixtures of valence and Rydberg character; for pyrrole and other molecules, the ramifications of such Rydberg-valence character on photodynamics have been discussed by Paterson and Townsend. 21 Initially, treating the methyl group as a point mass, the point group symmetry of NMP is C 2v .…”

“…The main focus here will be the vibrational and vibrationtorsional (vibtor) levels in the S 0 , S 1 , and D 0 + electronic states of NMP, building on our earlier two-dimensional LIF (2D-LIF) and zero-electron-kinetic energy (ZEKE) study that concentrated on the torsional levels 20 and where we reported the adiabatic ionization energy (AIE) as 64 250 ± 5 cm −1 . Here, we extend the earlier spectroscopic work to provide more definitive assignments of the S 1 levels, via both fluorescence and ZEKE spectroscopies.…”