Barrier to methyl internal rotation of cis- and trans-2-methylvinoxy radicals in the {approximately ovr X}({sup 2}A") and {approximately ovr B}({sup 2}A") states : experiment and theory.

Journal Article · Thu Nov 09 04:00:00 EST 2000 · J. Phys. Chem. A

DOI:https://doi.org/10.1021/jp002431+· OSTI ID:943106

Williams, S; Harding, L; Stanton, J; Weisshaar, J

The jet-cooled laser induced fluorescence spectrum of the {tilde B} {l_arrow} {tilde X} electronic transition of 2-methylvinoxy radical is assigned as a superposition of contributions from noninteracting cis and trans isomers. The spectrum of the cis isomer is identified by comparison with ab initio electronic structure calculations; both theory and experiment clearly indicate that the methyl conformation changes from the {tilde X} state to the {tilde B} state. Fits of both hot and cold bands to a one-dimensional torsional model yield methyl rotor barrier magnitudes of 270 {+-} 20 cm{sup -1} in the {tilde X} state and 200 {+-} 20 cm{sup -1} in the {tilde B} state. The ab initio calculations show that in the ground state the preferred conformation places one methyl CH bond in the plane of the molecular frame cis to the vicinal CC bond. Assignment of the spectrum of trans-2-methylvinoxy is more tentative because no resolved hot bands are available to corroborate the model. Our best estimate for the {tilde B} state barrier magnitude is 60 {+-} 15 cm{sup -1}. Multireference configuration interaction calculations and coupled cluster calculations are reasonably successful in obtaining methyl torsional barriers in agreement with experiment, although high accuracy is elusive for the {tilde B} state of both cis and trans isomers. By comparison with simpler cases, we infer that the {pi} radical character of the {tilde B}state strongly influences the methyl torsional barrier.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC; NSF
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 943106
• Report Number(s): ANL/CHM/JA-37523
• Journal Information: J. Phys. Chem. A, Journal Name: J. Phys. Chem. A Journal Issue: 44 ; Nov. 9, 2000 Vol. 104; ISSN 1089-5639; ISSN JPCAFH
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CONFIGURATION INTERACTION
ELECTRONIC STRUCTURE
GROUND STATES
ISOMERS
MATHEMATICAL MODELS
ONE-DIMENSIONAL CALCULATIONS
RADICALS
ROTATION