Does Ultraviolet Absorption Intensity Increase in Solution?

Abstract
Absolute absorption intensities and oscillator strengths were determined for isoprene and cis- and trans-piperylenes in the region 1750–2400A, in vapor and in n-heptane solution, using a vacuum fluorite spectrograph. More accurate oscillator strengths are obtained if our measurements at short wave-lengths are combined with the Beckman data of Shell Development Company at longer wave-lengths. For the three compounds the best values of the experimental Lorentz-Lorenz correction, or ratio of integrated intensities under the molar absorption curves for solution and vapor, were close to unity, a result obtained previously by Pickett and co-workers for cyclopentadiene and cyclohexadiene absorption in this same region. A value of 0.98±0.04 for this correction represents the mean of all five of these determinations. Although the values obtained from our data alone without using the Shell curves showed a much larger spread, every determination was substantially below the correction factor of 1.30 predicted by Chako's classical oscillator theory for this wave-length region and these solvents.