Photochemistry of Benzene Vapor at 1849 Å

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Abstract
The benzene‐disappearance quantum yield at 1849 Å and 1 torr has been determined to be 0.25±0.02 and independent of the number of absorbed quanta to ∼15% conversion. Nitrogen pressures from 0.1 to 50 atm reduce the disappearance yield. At 1 atm N2, the yield is reduced approximately fourfold. Addition of 200 torr propane reduces the yield more than one order of magnitude. At 2 and 3 torr benzene, the quantum yield is reduced to 0.13 and 0.10, respectively, and extrapolates at zero pressure to ∼1.0. Only two major products are found. One is volatile with structured absorption in the region 2600 to 2100 Å. Seventeen peaks are resolved in the spectrum with constant separation of ∼500 cm−1. Assuming that the initial yield of the product is equal to the disappearance yield of benzene, an oscillator strength of 0.2 is calculated for the band with maximum absorptivity of 8300 liters/mole·cm at 2350 Å. The compound is tentatively identified as an isomer of benzene. The second product is of high molecular weight and arises by polymerization of the volatile compound. It is suggested that the mechanism for benzene disappearance involves internal conversion to the ground electronic state with subsequent rearrangement to produce the benzene isomer.