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.