RESUMO
The absorption, fluorescence, and excitation spectra of free base tetraazaporphine (H2TAP) trapped in Ne, N2, and Ar matrices have been recorded at cryogenic temperatures. Normal Raman spectra of H2TAP were recorded in KBr discs and predicted with density functional theory (DFT) using large basis sets calculations. The vibrational frequencies observed in the Raman Spectrum exhibit reasonable agreement with those deduced from the emission spectra, as well as with frequencies predicted from large basis set DFT computations. The upper state vibrational frequencies, obtained from highly resolved, site selected excitation spectra, are consistently lower than the ground state frequencies. This contrasts with the situation in free base phthalocyanine, where the upper state shows little changes in vibrational frequencies and geometry when compared with the ground state. Investigations of the photochemical properties of H2TAP isolated in the three matrices have been performed using the method of persistent spectral hole-burning (PSHB). This technique has been used to reveal sites corresponding to distinct N-H tautomers which were not evident in the absorption spectra. An analysis of the holes and antiholes produced with PSHB in the Qx (0-0) absorption band made it possible to identify inter-conversion of distinct host sites.
RESUMO
Optical absorption spectra of thin film samples, formed by the codeposition of zinc vapor with D2 and CH4, have been recorded with synchrotron radiation. With sufficiently low metal vapor flux, samples deposited at 4 K were found to consist exclusively of isolated zinc atoms for both solids. The atomic absorption bands in the quantum solids D2 and CH4 were found to exhibit large bandwidths, behavior related to the high lattice frequencies of these low mass solids. The reactivity of atomic zinc was promoted with (1)P state photolysis leading to the first recording of electronic absorption spectra for the molecules ZnD2 and CH3ZnH in the vacuum ultraviolet (VUV) region. (3)P state luminescence of atomic zinc observed in the Zn/CH4 system points to the involvement of the spin triplet state in the relaxation of CH3ZnH system as it evolves into the C3v ground state. This state is not involved in the relaxation of the higher symmetry molecule ZnD2. Time dependent density functional theory (TD-DFT) calculations were conducted to predict the electronic transitions of the inserted molecular species. Comparisons with experimental data indicate the predicted transition energies are approximately 0.5 eV less than the recorded values. Possible reasons for the discrepancy are discussed. The molecular photochemistry of ZnD2 and CH3ZnH observed in the VUV was modeled successfully with a simple four-valence electron AH2 Walsh-type diagram.