High-resolution ultraviolet laser spectroscopy on jet-cooled benzene molecules: Ground and excited electronic state polarizabilities determined from static Stark effect measurements

Static electric polarizabilities of the S-0 ((1)A(1g)) ground electronic an d the vibronically excited 6(1)S(1) (B-1(2u)) state of benzene were measure d by applying ultraviolet (UV) laser Stark spectroscopy. The experimental s etup consisted of a frequency doubled tunable narrow-band continuous wave ( cw) laser system operating at 259 nm, a molecular beam apparatus, and a cap acitor capable of generating strong static and homogeneous electric fields up to 250 kV/cm. Experimental linewidths of less than 30 MHz were achieved for the rotational transitions, and Stark displacements of typically severa l 10 MHz could be detected. Stark patterns of 16 rotational lines were reco rded and analyzed under different field strengths. Validity of second-order perturbation theory was confirmed by the observed effects, and the diagona l components of the polarizability tensors could be adjusted by a weighted least-squares technique. Results were applied to calculating Stark spectra and comparing them to experimental data. Good agreement could be found, exc ept for an obscure singular perturbation within one rotational line. The ne w polarizabilities were compared to both experimental and theoretical resul ts in the literature. Ground state data are in general agreement, whereas n o comparable experimental work addressing the excited electronic state exis ts. Finally, polarizabilities of the beginning five polyacenes were compile d and compared with the benzene data. (C) 1999 American Institute of Physic s. [S0021-9606(99)02120-0].