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 $S_0{(}^1{A}_{\text{1g}})$ ground electronic and the vibronically excited $6^1{\mathrm{ S}}_1{(}^1{B}_{\text{2u}})$ state of benzene were measured by applying ultraviolet (UV) laser Stark spectroscopy. The experimental setup consisted of a frequency doubled tunable narrow-band continuous wave (cw) laser system operating at 259 nm, a molecular beam apparatus, and a capacitor 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 several 10 MHz could be detected. Stark patterns of 16 rotational lines were recorded and analyzed under different field strengths. Validity of second-order perturbation theory was confirmed by the observed effects, and the diagonal 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, except for an obscure singular perturbation within one rotational line. The new polarizabilities were compared to both experimental and theoretical results in the literature. Ground state data are in general agreement, whereas no comparable experimental work addressing the excited electronic state exists. Finally, polarizabilities of the beginning five polyacenes were compiled and compared with the benzene data.