Femtosecond degenerate four-wave mixing of cyclopropane

Femtosecond degenerate four-wave mixing (fs-DFWM) is applied for the measurement of rotational constants of cyclopropane (C3H6). The rotational coherence method yields a very accurate B-0=20 093.322(12) MHz and centrifugal distortion constants D-J and D-JK. To exploit the full resolution of the fs-DFWM method, the accuracy of the optical delay measurement was increased by nearly two orders of magnitude, including elimination of effects from the refractive index of air. The fs-DFWM molecular constants are comparable in accuracy to those from high-resolution infrared spectroscopy and are only surpassed by those of dipole distortion microwave spectroscopy. In parallel, the equilibrium structure, vibrationally averaged structure parameters and rotational constants were calculated using high-level ab initio methods and large basis sets. Combining these with the results of previous calculations and the measured rotational constants yields r(e)(C-C)=1.5034(3) A, r(e)(C-H)=1.0775(5) A, and alpha(e)(H-C-H)=115.09(10)degrees. (C) 2005 American Institute of Physics.