Photodissociation of pyrrole–ammonia clusters by velocity map imaging: mechanism for the H-atom transfer reaction

Abstract

The photodissociation dynamics of pyrrole-ammonia clusters (PyHÁ(NH 3 ) n , n = 2-6) has been studied using a combination of velocity map imaging and non-resonant detection of the NH 4 (NH 3 ) nÀ1 products. The excited state hydrogen-atom transfer mechanism (ESHT) is evidenced through delayed ionization and presents a threshold around 236.6 nm, in agreement with previous reports. A high resolution determination of the kinetic energy distributions (KEDs) of the products reveals slow (B0.15 eV) and structured distributions for all the ammonia cluster masses studied. The low values of the measured kinetic energy rule out the existence of a long-lived intermediate state, as it has been proposed previously. Instead, a direct N-H bond rupture, in the fashion of the photodissociation of bare pyrrole, is proposed. This assumption is supported by a careful analysis of the structure of the measured KEDs in terms of a discrete vibrational activity of the pyrrolyl co-fragment.

Fast Nonradiative Decay in o-Aminophenol

“…This is due to a bigger change in the excited state geometry of the cis isomer as a consequence of its geometry constraint. Thus, assuming an 17 equal population of both isomers, and owing the signal to noise ratio of the experiment, the cis isomer is indiscernible and nothing can be conclude about its intrinsic stability in the ground state.…”

Velocity map imaging of HBr photodissociation in large rare gas clusters

“…[8][9][10][11][12][13][14] When this experiment was moved to our laboratory in Prague, the studies have been extended to other systems, e.g., hydrogen halides on ice nanoparticles [15][16][17] or clusters of biologically relevant molecules. 23 There were only two recent studies, where also somewhat larger species were considered: e.g., pyrrole-ammonia 24 and N 2 O (Ref. When cluster effects were observed in photofragment images, it has been usually attributed exclusively to dimers, e.g., (CH 3 I) 2 , 20 (HI) 2 , 21 (ICN) 2 , 22 and pyrrole-Xe.…”

Can Hydrated Electrons be Produced from Water with Visible Light?

“…or quasi‐classical trajectory surface‐hopping simulations, e. g. [68–73] . For phenol⋅⋅⋅(NH 3 ) n , phenol⋅⋅⋅(H 2 O) n and pyrrole⋅⋅⋅(NH 3 ) n complexes, it was experimentally established that PCET from photoexcited pyrrole or phenol to the solvent molecules is the dominant process, [74–77] rather than proton transfer, as previously thought [78,79] …”

“…The kinetic energy distributions of H-atoms photodetached from pyrrole, phenol, indole, thiophenol, etc., were extensively investigated with velocity map imaging, multimass ion imaging, Rydberg tagging and femtosecond spectroscopy experiments, see [55][56][57][58][59][60] for representative examples. These experimen- tal studies were supported by ab initio calculations of the relevant PE surfaces and by calculations of the nonadiabatic time-dependent quantum wave-packet dynamics, e. g. [61][62][63][64][65][66][67] or quasi-classical trajectory surface-hopping simulations, e. g.. [68][69][70][71][72][73] For phenol•••(NH 3 ) n , phenol•••(H 2 O) n and pyrrole•••(NH 3 ) n complexes, it was experimentally established that PCET from photoexcited pyrrole or phenol to the solvent molecules is the dominant process, [74][75][76][77] rather than proton transfer, as previously thought. [78,79] The shape of the diffuse σ* orbital located on the NH group of HzH is similar to the shape of the σ* orbitals of pyrrole, phenol and indole.…”