A new method for investigating infrared spectra of protonated benzene (C _6H _7) and cyclohexadienyl radical (c-C _6H _7) using para-hydrogen

摘要

We use protonated benzene (C _6H _7) and cyclohexadienyl radical (c-C _6H _7) to demonstrate a new method that has some advantages over other methods currently used. C _6H _7 and c-C _6H _7 were produced on electron bombardment of a mixture of benzene (C _6H _6) and para-hydrogen during deposition onto a target at 3.2 K. Infrared (IR) absorption lines of C _6H _7 decreased in intensity when the matrix was irradiated at 365 nm or maintained in the dark for an extended period, whereas those of c-C _6H _7 increased in intensity. Observed vibrational wavenumbers, relative IR intensities, and deuterium isotopic shifts agree with those predicted theoretically. This method, providing a wide spectral coverage with narrow lines and accurate relative IR intensities, can be applied to larger protonated polyaromatic hydrocarbons and their neutral species which are difficult to study with other methods.