Theoretical Study On Vibronic Interactions And Photophysics Of Low-lying Excited Electronic States Of Polycyclic Aromatic Hydrocarbons

Samala, Nagaprasad Reddy

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https://hdl.handle.net/2142/50849 Copy

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Title

Theoretical Study On Vibronic Interactions And Photophysics Of Low-lying Excited Electronic States Of Polycyclic Aromatic Hydrocarbons

Author(s)

Samala, Nagaprasad Reddy

Contributor(s)

Mahapatra, S.

Issue Date

2014-06-19

Keyword(s)

Mini-symposium: Astronomical Molecular Spectroscopy in the Age of ALMA

Abstract

Polycyclic aromatic hydrocarbons (PAHs), in particular, their radical cation (PAH$^+$), have long been postulated to be the important molecular species in connection with the spectroscopic observations\footnote{J. Zhang et al., J. Chem. Phys., 128,104301 (2008).; F. Salama, Origins of Life Evol. Biosphere, 28, 349 (1998).; F. Salama et al., Planet. Space Sci., 43, 1165 (1995).; F. Salama et al., Astrophys. J., 526, 265 (1999).; J. Szczepanski et al., Chem. Phys. Lett., 232, 221 (1995).; J. Szczepanskiet al., Chem. Phys. Lett., 245, 539 (1995).; J. Zhang et al., Astrophys. J., 715, 485 (2010).} in the interstellar medium. Motivated by numerous important observations by stellar as well as laboratory spectroscopists, we undertook detailed quantum mechanical studies of the structure and dynamics of electronically excited PAH$^+$~in an attempt to establish possible synergism with the recorded data\footnote{V. Sivaranjana Reddy et al., Phys. Rev. Lett, 104, 111102 (2010).; S. Ghanta et al., Phys. Chem. Chem. Phys. 13, 14523.; \&~13, 14531 (2011).}. In this study, we focus on the quantum chemistry and dynamics of the doublet ground (X) and low-lying excited (A, B and C) electronic states of the radical cation of tetracene (Tn), pentacene (Pn), and hexacene (Hn) molecule. This study is aimed to unravel photostability, spectroscopy, and time-dependent dynamics of their excited electronic states. In order to proceed with the theoretical investigations, we construct suitable multistate and multimode Hamiltonian for these systems with the aid of extensive ab initio calculations of their electronic energy surfaces. The diabatic coupling surfaces are derived from the calculated adiabatic electronic energies. First principles nuclear dynamics calculations are then carried out employing the constructed Hamiltonians and with the aid of time-independent and time-dependent quantum mechanical methods\footnote{S. Nagaprasad Reddy et al., J. Phys. Chem. A., 117, 8737 (2013).}. We compared our theoretical results with available photoelectron spectroscopy, zero kinetic energy photoelectron (ZEKE) spectroscopy and matrix isolation spectroscopy (MIS) results. A peak at 8650 \AA{} in the B state spectrum of Tn$^+$~is in good agreement with the DIB at 8648 \AA{} observed by Salama et al. Similarly in Pn$^+$, a peak at 8350 \AA{} can be correlated to the DIB at 8321 \AA{} observed by Salama et al.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/50849

DOI

https://doi.org/10.15278/isms.2014.RA11

Copyright and License Information

Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/

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