AB-INITIO STUDIES OF THE DIPOLE POLARIZABILITIES OF CONJUGATED MOLECULES .4. THE DIPOLE POLARIZABILITY AND 1ST HYPERPOLARIZABILITY OF O-BENZYNE AND RELATED MOLECULES

We report ab initio SCF and Moller-Plesset MP2 calculations of the sta tic dipole polarizability and SCF calculations of the first hyperpolar izability tensors of o-benzyne. The standard STO/6-31G basis set was a ugmented with s and p diffuse functions and multiple d polarization fu nctions on the carbon atoms. Further p functions were also added on th e hydrogen atomic centres. We compare the results for this molecule wi th those for ethyne, allene and s-cis-butadiene, for which we also rep ort new polarizability tensor calculations. Comparison is made with ex periment where possible. Using the largest basis set STO/6-31 + G(3d,3 p) at the SCF level of theory, the alpha tensor components for o-benzy ne were alpha(xx) = 41.80 u, alpha(yy) = 70.37 u and alpha(zz) = 82.8 u. The corresponding components of beta were 146.2, 36.3 and 9.7 u res pectively. The MP2 procedure gives negligible improvements on the SCF average dipole polarizability predictions by using the STO/6-31 + G(d, p) basis set. We show that o-benzyne should be considered as a potenti al reagent for the design and synthesis of new non-linear optical mate rials. Our results could also be useful for the identification of this transient molecule in non-linear optical experiments.