Ultrafast excitation of out-of-plane vibrations and vibrational energy redistribution after internal conversion of 4-nitroaniline

Abstract

Articles you may be interested inHigh resolution IR diode laser study of collisional energy transfer between highly vibrationally excited monofluorobenzene and CO2: The effect of donor fluorination on strong collision energy transfer Theoretical investigation of highly excited vibrational states in DFCO: Calculation of the out-of-plane bending states and simulation of the intramolecular vibrational energy redistribution Mode dependent intracluster vibrational energy redistribution rate in size-selected benzonitrile-( CHCl 3 ) n=1-3 clusters A quantum mechanical study of the role of out-of-plane vibrations in benzene in the intramolecular redistribution of vibrational energy Ultrafast vibrational excitation and energy redistribution in the electronic ground state after internal conversion of 4-nitroaniline ͑PNA͒ and isotope labeled analogs is investigated by picosecond anti-Stokes resonance Raman spectroscopy. In PNA, PNA-di-15 N and PNA-D 4 , anti-Stokes Raman lines of overtones and/or combination bands of out-of-plane vibrations display risetimes close to the decay time of the electronically excited state of about 0.5 ps and pronounced excess populations. Compared to such fast dynamics, the strongly Raman active totally-symmetric modes show a considerably slower picosecond rise time. Our results indicate primary excitation of out-of-plane vibrations by internal conversion and secondary excitation of strongly Raman active vibrations by redistribution of the vibrational energy.

Energy Flow in Push–Pull Chromophores: Vibrational Dynamics in para‐Nitroaniline

“…No evidence for conformational or other inhomogeneous broadening in PNA in DMSO, a polar solvent, emerged, in alignment with RREP analysis. [17] Qualitative and quantitative aspects of the vibrational dynamics confirm the reports of Werncke et al [28,29] However, a careful evaluation of the details of the evolution shows some interesting, and previously unreported, mode-specific vibrational decay rate constants. Little effect of l EX on these lifetimes was discovered.…”

“…[28,29] These authors showed that PNA behaves in a manner contrary to the interpretation of rapid thermalization and vibrational cooling proposed by Ernsting et al [24][25][26] The findings support the important role of out-of-plane NO 2 motion in IC, and show nonthermal vibrational energy distributions, particularly among the higher frequency modes, persisting for 6-7 ps. The kinetics of both IVR and VR were slower in TRARRS experiments than in the less direct TRA studies.…”

“…This approach has been used for PNA by others. [28,29] Under conditions of resonance, however, analysis is complicated by different cross-sections for Stokes and anti-Stokes scattering. It will not be evaluated here.…”

“…The electronic portions of this photocycle and their dependence on solvent polarity have been studied by several groups; [23][24][25][26] a model has emerged that is well-accepted in broad strokes, though some details remain in dispute. The associated vibrational dynamics have not reached as thorough a consensus, [24][25][26][27][28][29] and it is these dynamics that are probed here. Excitation of PNA to the CT state is followed by evolution on S 1 and rapid internal conversion (IC) back to S 0 .…”

“…[23,24] Vibrational dynamics have been explored as well. [24][25][26][27][28][29] Semi-empirical computations (SAM1) suggest that NO 2 twisting is an important coordinate involved in S 0 ! S 1 IC, [24][25][26] supported by recent molecular dynamics simulations.…”