Ultraviolet resonance Raman study of the pyrene S4, S3, and S2 excited electronic states

Abstract

UV resonance Raman excitation within the S2, S3, and S4 π→π* electronic transitions of pyrene results in strong enhancement of totally symmetric ring vibrations. The Raman modes most strongly enhanced within these electronic transitions derive from vibrations exhibiting Franck–Condon vibronic structure in the absorption spectrum. The 1597 cm−1 (b3g) mode shows selective enhancement between the S3 and S4 transitions, and between the S2 and S3 transitions due to Herzberg–Teller coupling between these symmetry-allowed states. The experimentally observed S4 resonance Raman excitation profiles of the totally symmetric pyrene fundamentals agree closely with those calculated using resonance Raman transform theory if non-Condon contributions are included. We see an increased non-Condon contribution with an increasing vibrational frequency, indicating nonadiabatic vibronic interactions. The high incident energy fluxes of the Nd-YAG laser-based excitation source cause saturation of the pyrene Raman intensities since molecular absorption depletes the ground state population. The long-lived S1 singlet excited state bottlenecks relaxation back to the ground electronic state. Formation of pyrene phototransients is also observed with high incident energy fluxes at particular excitation wavelengths.

Achievements in resonance Raman spectroscopy

“…Other features of RRS are not yet well predicted by theoretical approaches: pyrene solutions excited under resonance conditions show unusually strong overtones and combination bands, especially when exciting into a vibrational region of an absorption band, and much less so when exciting into an origin band [77,78]. As an illustration, Fig.…”

Heat capacity prediction for polynuclear aromatic solids using vibration spectra

“…The experimental frequency data set obtained by combining results from Jones and Asher [38], Joblin et al [39] and De Frees et al [40], comprises only 56 frequencies and is inadequate for C p prediction. Computational results from Bree et al [41] benchmarked against these experimental data and comprising the requisite 72 frequencies yields C p values in close agreement with the experimental ones and the values for the parameters θ D , q and A 0 follow the expected trend (Table 1).…”

Evidence of neutral radical induced analyte ion transformations in APPI and Near-VUV APLI

“…Computational simulation of the resulting charged product distribution recorded after a reaction time of 23 ms requires an estimate of the initial pyrene radical cation concentration. The radical cation concentration [M •ϩ ] generated within one laser pulse via a (1ϩ1) REMPI process is calculated using eq 5: The excitation of pyrene at 193 nm results in initial population of the S 4 state, which relaxes to the S 1 manifold on the ps time-scale [38]. The S 1 state has an estimated lifetime of Ϸ 100 ns [38 -43], which is 10 times larger than the laser pulse width.…”