title: Rotational constants and structure of para-difluorobenzene determined by femtosecond Raman coherence spectroscopy: A new transient type.
abstract: Femtosecond Raman rotational coherence spectroscopy (RCS) detected by degenerate four-wave mixing is a background-free method that allows to determine accurate gas-phase rotational constants of non-polar molecules. Raman RCS has so far mostly been applied to the regular coherence patterns of symmetric-top molecules, while its application to nonpolar asymmetric tops has been hampered by the large number of RCS transient types, the resulting variability of the RCS patterns, and the 10(3)-10(4) times larger computational effort to simulate and fit rotational Raman RCS transients. We present the rotational Raman RCS spectra of the nonpolar asymmetric top 1,4-difluorobenzene (para-difluorobenzene, p-DFB) measured in a pulsed Ar supersonic jet and in a gas cell over delay times up to ∼2.5 ns. p-DFB exhibits rotational Raman transitions with ΔJ = 0, 1, 2 and ΔK = 0, 2, leading to the observation of J -, K -, A -, and C-type transients, as well as a novel transient (S-type) that has not been characterized so far. The jet and gas cell RCS measurements were fully analyzed and yield the ground-state (v = 0) rotational constants A0 = 5637.68(20) MHz, B0 = 1428.23(37) MHz, and C0 = 1138.90(48) MHz (1σ uncertainties). Combining the A0, B0, and C0 constants with coupled-cluster with single-, double- and perturbatively corrected triple-excitation calculations using large basis sets allows to determine the semi-experimental equilibrium bond lengths re(C1-C2) = 1.3849(4) Å, re(C2-C3) = 1.3917(4) Å, re(C-F) = 1.3422(3) Å, and re(C2-H2) = 1.0791(5) Å.
authors.affiliation: Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3000 Bern 9, Switzerland.
authors.forename: Takuya
authors.initials: T
authors.lastname: Den
authors.affiliation: Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3000 Bern 9, Switzerland.
authors.forename: Hans-Martin
authors.initials: HM
authors.lastname: Frey
authors.affiliation: Department of Chemistry and Biochemistry, University of California at Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095-1569, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Felker
authors.affiliation: Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3000 Bern 9, Switzerland.
authors.forename: Samuel
authors.initials: S
authors.lastname: Leutwyler
mesh_terms: D005464:Fluorobenzenes / Q000737:chemistry*; D015394:Molecular Structure; D012399:Rotation; D013059:Spectrum Analysis, Raman; D013997:Time Factors
chemical_list: D005464:Fluorobenzenes