Hindered internal rotation and torsion{endash}vibrational coupling in ortho-chlorotoluene ({ital S}{sub 1}) and ortho-chlorotoluene{sup +} ({ital D}{sub 0})

Journal Article · Fri Mar 01 04:00:00 EST 1996 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.471198· OSTI ID:278935

Richard, E C; Walker, R A; Weisshaar, J C ^[1]

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1. Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706-1396 (United States)

The techniques of resonant two-photon ionization (R2PI) and pulsed field ionization (PFI) were used to measure absorption spectra of ortho-chlorotoluene ({ital S}{sub 1}, {tilde {ital A}}{sup 1}{ital A}{sub 1}) and of ortho-chlorotoluene{sup +} ({ital D}{sub 0}, {tilde {ital X}}{sup 2}{ital A}{sub 1}; the cation ground state) for internally cold molecules in a pulsed nozzle expansion. The adiabatic ionization potential is 71318{plus_minus}5 cm{sup {minus}1}=8.8423{plus_minus}0.0006 eV. Most of the observed low lying torsion{endash}vibrational structure in both {ital S}{sub 1} and {ital D}{sub 0} can be assigned using a one-dimensional torsional model plus low frequency vibrational modes whose identity is corroborated by the {ital ab} {ital initio} normal modes of {ital D}{sub 0}. The intensities of certain weak, forbidden torsion{endash}vibration combination bands in the {ital S}{sub 1}{endash}{ital S}{sub 0} spectrum are well predicted by a nuclear coordinate dependence of the electric dipole transition moment. The threefold methyl torsional barrier is {ital V}{sub 3}=144.2{plus_minus}2.0 cm{sup {minus}1} in {ital S}{sub 1} and {ital V}{sub 3}=456.5{plus_minus}2.0 cm{sup {minus}1} in {ital D}{sub 0}. {ital Ab} {ital initio} calculations at the HF/6-31G{asterisk} level find {ital V}{sub 3}=481 cm{sup {minus}1} in {ital S}{sub 0} with the minimum energy conformation pseudo-{ital trans}, i.e., with one CH bond lying in the plane of the ring on the opposite side of the chlorine substituent. Spectral band intensities show that the minimum is pseudo-{ital trans} in {ital S}{sub 1} and {ital D}{sub 0} as well. In both {ital S}{sub 1} and {ital D}{sub 0}, excitation of either of the two lowest frequency out-of-plane bending modes, {nu}{sub 38} or {nu}{sub 37}, leaves the methyl torsional potential essentially unchanged. (Abstract Truncated)

• DOE Contract Number: FG02-92ER14306
• OSTI ID: 278935
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 12 Vol. 104; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ABSORPTION SPECTRA
CATIONS
CHLORINATED AROMATIC HYDROCARBONS
COUPLING
GROUND STATES
PHOTOIONIZATION
POTENTIALS
ROTATION-VIBRATION MODEL
TOLUENE
TORSION