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An experimental and ab initio investigation of the low-frequency vibrations of coumaran

Watkins, M.J., Belcher, D.E. and Cockett, M.C.R. (2002) An experimental and ab initio investigation of the low-frequency vibrations of coumaran. Journal of Chemical Physics, 116 (18). pp. 7855-7867. ISSN 0021-9606

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Coumaran (2,3-dihydrobenzofuran) has been studied using a combination of (1 + 1) resonantly enhanced multiphoton ionization (REMPI) and zero electron kinetic energy (ZEKE) studies, supported by ab initio molecular orbital calculations, in order to characterize the low wave number vibrational structure of the S1 neutral excited and D0 ionic ground states. These studies focus primarily on the modifying effects of electronic excitation and ionization on the balance of forces driving the S1 and D0 equilibrium structures toward or away from planarity. The results suggest that coumaran retains a puckered structure in the S1 state, having a barrier significantly smaller than that in the electronic ground state, but is apparently pseudo-planar or weakly puckered in the cation ground state. In each state the drive towards or away from planarity results from a competition between decreasing bond order in the aromatic system which increases torsional interactions thereby favoring a higher barrier and an increase in bond order in the furan ring which has the opposite effect. The lack of symmetry in coumaran lifts any restrictions on which out-of-plane modes can couple, resulting in a rich combination band structure in REMPI and ZEKE spectra, principally involving the ring twisting (44) and the ring pucker (45) vibrational modes. The butterfly mode (43) on the other hand shows surprisingly little activity.

Item Type: Article
Institution: The University of York
Academic Units: The University of York > Chemistry (York)
Depositing User: York RAE Import
Date Deposited: 23 Apr 2009 15:02
Last Modified: 23 Apr 2009 15:02
Published Version: http://dx.doi.org/10.1063/1.1468315
Status: Published
Publisher: American Institute of Physics
Identification Number: 10.1063/1.1468315
URI: http://eprints.whiterose.ac.uk/id/eprint/6578

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