Probing the electronic structure and spectroscopy of pyrrolyl and imidazolyl radicals using high-resolution photoelectron imaging of cryogenically cooled anions

Abstract

High-resolution photoelectron imaging and photodetachment spectroscopy of cryogenically-cooled pyrrolide and imidazolide anions are used to probe the electronic structure and spectroscopy of the pyrrolyl and imidazolyl radicals. The high-resolution data...

Probing the Strong Nonadiabatic Interactions in the Triazolyl Radical Using Photodetachment Spectroscopy and Resonant Photoelectron Imaging of Cryogenically Cooled Anions

“…In principle, Rydberg spectroscopy is more general and can be used for any neutral molecules, whereas DBSs can only exist in polar anions. However, the Rydberg spectroscopy can be very complicated due to the presence of multiple Rydberg states and has been applied to relatively simple molecules. , A single DBS usually exists for polar anions, allowing relatively large anions to be investigated. − Recently, we have initiated a series of studies to obtain high-resolution PES data for the azolide anions using high-resolution cryogenic ESI-PEI. , It turned out that pyrrolide and imidazolide do not support DBSs because the dipole moments of the corresponding pyrrolyl and imidazolyl radicals are below the empirical critical value (∼2.5 D) . Nevertheless, the high-resolution PEI data still yielded considerably more vibronic fine features and vibrational information .…”

Dipole-Bound State, Photodetachment Spectroscopy, and Resonant Photoelectron Imaging of Cryogenically-Cooled 2-Cyanopyrrolide

“…33 Recently, we reported a high-resolution photoelectron imaging (PEI) and threshold photodetachment (PD) study of the pyrrolide anion (C 4 NH 4 − ). 35 However, we did not observe a DBS for pyrrolide because the dipole moment of the pyrrolyl radical (2.18 D) is below the critical dipole moment to support a DBS. Substituting one of the H atoms on the αposition by a CN group in pyrrolyl should significantly increase the dipole moment of the resulting 2-cyannopyrrolyl radical, making it possible for the 2-cyanopyrrolide anion (2-CNPyr − ) to support a DBS.…”

“…It should be pointed out that this threshold behavior is completely different from that of the parent pyrrolide, which shows that the d partial wave is dominant near the threshold. 35 The π HOMOs of the two anions are similar, except that the HOMO of 2-CNPyr − has some contribution from the CN group (Figure 2). The d wave dominance in pyrrolide made it very challenging to take high-resolution PE images near threshold because of the extremely low detachment threshold.…”

“…This behavior is very different from the PDS of pyrrolide, in which the d-wave dominates in the threshold and no step was observed. 35 The weak below-threshold peak 0 at 24 748 cm −1 (3.0981 eV), observed due to resonant two-photon photodetachment (R2PD), indicates the existence of a DBS. It should correspond to the zero-point level of the DBS with a binding energy of 240 ± 5 cm −1 (0.0298 ± 0.0006 eV) defined by its separation from the detachment threshold.…”

“…In this article, we report an investigation of cryogenically cooled 2-CNPyr − using PDS and rPES and our observation of the DBS, allowing us to obtain fundamental frequencies for 19 vibrational modes (out of a total of 24) of the 2-CNPyr radical, whereas only eight vibrational frequencies (out of a total of 21) were obtained for the pyrrolyl radical in the recent PEI study. 35 Five-membered heterocyclic pyrroles and their derivatives have attracted broad interest because of their presence in many biologically important molecules. 36,37 The pyrrole derivative, 2cyanopyrrole, with a CN group in the α-position, is an important intermediate in the synthesis of porphyrins.…”