title: Femtosecond rotational Raman coherence spectroscopy of cyclohexane in a pulsed supersonic jet.
abstract: We combine the technique of femtosecond degenerate four-wave mixing (fs-DFWM) with a high repetition-rate pulsed supersonic jet source to obtain the rotational coherence spectrum (RCS) of cold cyclohexane (C(6)H(12)) with high signal/noise ratio. In the jet expansion, the near-parallel flow pattern combined with rapid translational cooling effectively eliminate dephasing collisions, giving near-constant RCS signal intensities over time delays up to 5 ns. The vibrational cooling in the jet eliminates the thermally populated vibrations that complicate the RCS coherences of cyclohexane at room temperature [Brügger, G.; et al. J. Phys. Chem. A 2011, 115, 9567]. The rotational cooling reduces the high-J rotational-state population, yielding the most accurate ground-state rotational constant to date, B(0) = 4305.859(9) MHz. Based on this B(0), a reanalysis of previous room-temperature gas-cell RCS measurements of cyclohexane gives improved vibration-rotation interaction constants for the ν(32), ν(6), ν(16), and ν(24) vibrational states. Combining the experimental B(0)(C(6)H(12)) with CCSD(T) calculations yields a very accurate semiexperimental equilibrium structure of the chair isomer of cyclohexane.
authors.affiliation: Departement für Chemie und Biochemie, Universität Bern, Bern, Switzerland.
authors.forename: Georges
authors.initials: G
authors.lastname: Brügger
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Frey
authors.forename: Patrick
authors.initials: P
authors.lastname: Steinegger
authors.forename: Philipp
authors.initials: P
authors.lastname: Kowalewski
authors.forename: Samuel
authors.initials: S
authors.lastname: Leutwyler