Ultrasonic frequency shifts close to the first order and tricritical phase transitions in NH4Cl

Photochemical reaction between biphenyl and carbon tetrachloride is studied with nanosecond time-resolved infrared spectroscopy and picosecond time-resolved fluorescence spectroscopy. Fluorescence lifetime of biphenyl in carbon tetrachloride solutions is measured with a picosecond time-resolved fluorescence spectrometer. The recorded lifetime is 3.8 ps, shorter than fluorescence lifetime in cyclohexane by a factor of four thousand. After the photoexcitation of biphenyl in carbon tetrachloride, the trichloromethyl (CCl3) radical is formed as a reaction intermediate, which is confirmed by the detection of the radicalʹs 896 cm-1 infrared band with nanosecond time-resolved infrared spectroscopy. One of the Cl atoms in solvent carbon tetrachloride is transferred to biphenyl to form the CCl3 radical and a biphenyl–Cl adduct. Together with the already reported spectroscopic detection of the CCl3 radical as an intermediate in photochemical reactions of trans-stilbene or anthracene with carbon tetrachloride, it is likely that this series of reactions are common for aromatic molecules.