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The fluorescence properties of 4-methyl-2,6-diacetylphenol (MAOH) are examined in 3-methylpentane and quantum yield measurements are made at room temperature and 77 K. The fluorescence quantum yield is temperature and excitation wavelength dependent. The emission properties of MAOH at 77 K have been examined in relation to those of 4-methyl-2,6-diformylphenol (MFOH). At this temperature, unlike MFOH, MAOH does not show any phosphorescence in 3-methylpentane. From this observation it is confirmed that phosphorescence appears due to the rotation of the formyl group in MFOH. The fluorescence decay rate of MAOH is relatively faster than that of MFOH and non-radiative decays are dominant in the decay processes of the excited states of both compounds.

Fluorescence spectra and lifetime of the phenyldimethylsilyl radical produced by photolysis of phenyltrimethylsilane have been determined in 3-methylpentane at 77 K.

CH-stretching overtone spectra of 3-methylpentane are measured for both liquid and low temperature (77 K) solid phases. A local-mode analysis is used to extract the diagonal local-mode anharmonicity constant. The results show that the local vibrational potential is more harmonic at high viscosity.

When the temperature of a photoionized TMPD-3MP glassy solution is suddenly raised from 77 K to 77 K + Δ T (Δ T ∼ 1 K), the recombination luminescence is enhanced, goes through a broad maximum and starts decaying. This is interpreted in terms of glass relaxation on warming. By means of a formally described model, the activation energy for electron detrapping is found to be 0.65 eV. In our opinion this large value indicates that electron detrapping is due to slow molecular rearrangements in the matrix.

The ESR spectrum of the radical cation of 3-methylpentane (3-MP) in CFCl2CF2Cl has been obtained. The spectrum is almost identical to that for the 2-methylbutane radical cation. From the spectral analysis it is concluded that 3-MP+ has a GT skeletal conformation and the unpaired electron is confined to the C3-C4 bond giving rise to large hyperfine couplings for the trans C-Hβ protons attached to the C2,C5 and C6 atoms, where C6, is on the side of the 3-methyl carbon atom. The results are totally consistent with concepts previously established from studies on the methyl-substituted propane and butane radical cations.

When trapped electrons produced in glassy 3-methylphentane by γ irradiation or by photoionization of tetramethyl-p-phenylenediamine are exposed to 700–1000 nm light at 72°K, their spectrum (λmax = ca. 1600nm) is red-shifted. Following illumination the shift reverses slowly over minutes. At 23°K the red-shift is relatively stable.

The spectra of e − t produced in 3-MP and MCH at 4°K were at longer wavelengths than those at 73°K, and shifted back to the same position as those produced at 73°K when the glasses were warmed to 73°K. The spectra in 3-MHX at 4 and 73°K were the same.

Based on an emission study of xanthone at ≈2 and 77°K it is concluded that the “dual” phosphorescence at 77°K in a 3-methylpentane glass matrix is due to emission from two n, π ∗ triplet states of xanthone. The two triplet states and their respective ground states are distinguished by their different molecular geometries.

A study of the photochemistry of a dilute rigid solution of durene in 3-methylpentane at 77°K reveals the presence of an independent one photon process in competition with the biphotonic process for β-bond cleavage at energies corresponding to excited vibrational levels of the first excited singlet state. In contrast, the photoionization of durene remains a two photon process over the entire energy range examined.