title: Missing levels lead to additional lines: the influence of nuclear spin statistics on femtosecond degenerate four wave mixing spectroscopy of polyatomic systems.
abstract: We present the results of comprehensive experimental and theoretical studies of the effect of nuclear spin statistics on the structure of rotational recurrences in femtosecond degenerate four-wave mixing (fs DFWM) spectra of asymmetric top molecules. New recurrences of J-type with a period of 1/[4(B + C)] are identified in fs DFWM spectra of near-prolate tops SO2 [H. M. Frey, P. Beaud, T. Gerber, B. Mischler, P. P. Radi and A. P. Tzannis, J. Raman Spectrosc., 2000, 31, 71] and NO2 [I. Pastirk, M. Comstock and M. Dantus, Chem. Phys. Lett., 2001, 349, 71]. Our measurements of the asymmetric oblate-like top CH3NO2 revealed new recurrences of A-type with a period of 1/(8A), A, B and C being the rotational constants.The incorporation of nuclear spin statistics into the fs DFWM simulation-fitting code allowed us to successfully reproduce all these new features and the subsequent theoretical analyses uncovered mechanisms of their appearance. The nuclear spin statistics is shown to have a profound effect on fs DFWM spectra of asymmetric top species, notably with several zero spin nuclei.
authors.affiliation: Johann Wolfgang Goethe-University Frankfurt/M., Institute of Physical and Theoretical Chemistry, Marie-Curie-Str. 11, D-60439 Frankfurt/M, Germany. riehn@chemie.uni-frankfurt.de
authors.forename: C
authors.initials: C
authors.lastname: Riehn
authors.forename: M I
authors.initials: MI
authors.lastname: Kunitski
authors.forename: V V
authors.initials: VV
authors.lastname: Matylitsky
authors.forename: M F
authors.initials: MF
authors.lastname: Gelin
authors.forename: B
authors.initials: B
authors.lastname: Brutschy