AB initio calculations of oscillator and rotatory strengths in the random-phase approximation: planar and twisted butadiene

Minimal basis set (STO-4G) ab initio calculations in the random-phase approximation (RPA) are presented for the ordinary and rotatory intensities of the low-lying electronic transitions of twisted cis-butadiene, and planar trans-butadiene. The formally equivalent intensities agree much better in the RPA than in either monoexcited CI or Hartree-Fock virtual orbital calculations. Comparisons with other work are given, and an explanation is suggested for the sensitivity of the rotatory strengths to substituents.