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Bending Vibrational Levels in the Electronic Spectra of Small Radicals
Author(s) -
Hsu YenChu
Publication year - 2018
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.201700370
Subject(s) - chemistry , vibronic coupling , ab initio , bending , symmetry (geometry) , atomic physics , radical , molecule , coupling (piping) , molecular vibration , spectral line , ab initio quantum chemistry methods , computational chemistry , spectroscopy , vibration , molecular physics , quantum mechanics , physics , thermodynamics , geometry , mechanical engineering , mathematics , organic chemistry , engineering
The role played by bending vibrations in the spectroscopy of small carbon‐containing radicals is illustrated by the patterns and effects shown by C 3 , CCH, and C 3 Ar. Because of the large change in the bending frequency between the X ˜ 1 Σ + g and A ˜ 1 Π u states of C 3 , the A ˜ 1 Π u state provides one of the best known examples of the coupling of electronic and vibrational motion in linear molecules (the Renner–Teller effect). The X ˜ 2 Σ + and A ˜ 2 Π states of CCH provide a classic instance of vibronic coupling between two close‐lying electronic states, which leads very rapidly to a chaotic pattern of mixed‐state vibrational energy levels, which can only be understood by extensive high‐quality ab initio calculations. C 3 Ar is an approximately T‐shaped molecule with no less than four large‐amplitude vibrations. Its A ˜ state provides a beautiful example of what happens to the angular momentum of a Π state of C 3 when the symmetry is lowered by complex formation.