Pulse Radiolysis Study of the Formation of Triplet Excited States of Naphthalene, Anthracene, and Biphenyl in Cyclohexane Vapor

Abstract

The first triplet excited state of naphthalene is produced in significant amounts when cyclohexane–naphthalene mixtures are pulse irradiated in the gas phase (120°C). The yield is independent of naphthalene concentration from 0.15 mole % up to at least 3.5 mole %, and can be decreased by about 95% by SF₆, CCl₄, C₆H₅CH₂Cl, CH₃Br, NH₃, and H₂O. The scavengeable part of the triplet yield is attributed to neutralization of the ion C₁₀H₈⁺ (which is formed by charge transfer from cyclohexane positive ion) by C₁₀H₈⁻ which is itself formed by electron capture. The scavengers compete with naphthalene for positive ions or for electrons. The rate‐constant ratios at 120°C for the reaction of the positive ions from cyclohexane with naphthalene and NH₃, $\mathrm{K(}{\mathrm{RH}}^{+}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{C}}_{10}{\mathrm{H}}_8\mathrm{)\hspace{0.17em}/\hspace{0.17em}k(}{\mathrm{RH}}^{+}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{NH}}_3\text{)\hspace{0.17em}=\hspace{0.17em}0.8\hspace{0.17em}±\hspace{0.17em}0.2}$ , and for electron capture by naphthalene and benzyl chloride, ${\mathrm{k(e}}^{-}\mathrm{\hspace{0.17em}+\hspace{0.17em}}{\mathrm{C}}_{10}{\mathrm{H}}_8{\mathrm{)\hspace{0.17em}/\hspace{0.17em}k(e}}^{-}\mathrm{\hspace{0.17em}+\hspace{0.17em}}\mathrm{BzCl}\text{)\hspace{0.17em}=\hspace{0.17em}3.0\hspace{0.17em}±\hspace{0.17em}0.5}$ , are obtained from competition studies. The triplet state of biphenyl observed in cyclohexane–biphenyl (0.2 mole %) is completely eliminated by SF₆ (1 mole %). In cyclohexane–naphthalene–anthracene mixtures, energy transfer from triplet naphthalene to anthracene is observed.