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Low‐lying singlet excited states of isocyanogen
Author(s) -
Ringer Ashley L.,
Sherrill C. David,
King Rollin A.,
Crawford T. Daniel
Publication year - 2008
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.21586
Subject(s) - excited state , coupled cluster , atomic physics , singlet state , excitation , chemistry , physics , quantum mechanics , molecule
Recent photofragment fluorescence excitation (PHOFEX) spectroscopy experiments have observed the à 1 A ″ singlet excited state of isocyanogen (CNCN) for the first time. The observed spectrum is not completely assigned and significant questions remain about the excited states of this system. To provide insight into the energetically accessible excited states of CNCN, optimized geometries, harmonic vibrational frequencies, and excitation energies for the first three singlet excited states are determined using equation‐of‐motion coupled‐cluster theory with singles and doubles (EOM‐CCSD) and correlation‐consistent basis sets. Additionally, excited state coupled‐cluster methods which approximate the contributions from triples (CC3) are utilized to estimate the effect of higher‐order correlation on the energy of each excited state. For the à 1 A ″ state, our best estimate for T 0 is about 42,200 cm −1 , in agreement with the experimentally estimated upper limit for the zero‐point level of 42,523 cm −1 . © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008