Electron spin echoes of a photoexcited triplet: Pentacene in p-terphenyl crystals

Electron spin echo observations of the photoexcited triplet state of 0.1 mol % pentacene-h14 and -d14 in p-terphenyl crystals at room temperature are presented. Theory is presented for calculation of the echo envelope modulations for an S = 1, I = 1/2 spin system including zero field splittings in the high field limit. Echo envelope modulations due to proton and deuteron hyperfine interactions in the pentacene molecule have been observed. The echo decay data are used to calculate triplet state decay parameters.