| The matrix isolation (MI) technique provides an inert medium for studying fragile or reactive species via spectroscopic means. In this work, we utilized the MI approach in combination with infrared absorption spectroscopy, in an attempt to explore chemical systems of interest in astrochemical processes and materials science.;In the first project, atomized Ni vapor was deposited with the polycyclic aromatic hydrocarbons (PAHs) naphthalene, fluorene, pyrene, or coronene onto a cold deposition surface with excess Ar (~12 K). Vibrational spectra were recorded for each Ni/PAH matrix, and compared with quantum-chemical calculations at the density-functional theory (DFT) level. It was found that all Ni-PAH's had a &eegr;6 coordination conformer that matched best with theory, the Ni state of the complexes were singlet, and structures had relatively high dissociation energies (~ 2 eV). For Ni-pyrene and Nicoronene, however, the matching conformer was not the predicted lowest energy structure. Several different functionals/bases (MPW1PW91/6-311++G(d,p), MPW1PW91/6-31+G(d,p), BPW91/LanL2DZ, and M06-L/LanL2DZ) were compared and it was found that MPW1PW91/6-311++G(d,p) matched the best.;For the second project, we investigated the proposed mechanism for H2 formation in the interstellar medium (ISM) upon photolysis of PAHs. As an example, 5,12-dihydrotetracene (DHT) was trapped in a matrix of excess argon (~12 K) and irradiated for up to 36 hours with a mercury lamp (253.6 nm). Infrared spectra of the matrix were taken before and after UV irradiation, showing that tetracene, and thus presumably molecular H2, were formed. These results were supported by transition state calculations, indicating a barrier of 2.595 eV. Nonetheless, given the relatively low conversion rate of ~22 % at 36 hours, which is equivalent to ~2 billion years in the (ISM), this process is unlikely to be important in the formation of H2 in the ISM.;In the final project, we present a hybrid mass spectrometer/matrix isolation instrument that was designed to generate and trap fragile cation radical diamondoid species into an inert Ar matrix. The system was capable of generating a high current of low-energy, mass-selected ions, and to direct that ion beam onto a cryogenic surface. To maintain charge neutrality of the matrix, the use of an electron "scavenger" species (e.g. CCl4) was employed; in addition, the simultaneous deposition of counter-ions into the matrix was attempted. Our results indicated that ions could be guided onto the matrix, but that they were being neutralized through some unknown mechanism(s). Due to the high vapor pressures of the molecular species that were investigated, a high background of neutral deposition obfuscated the rate of ion deposition in these experiments. In collaborative experiments on a related set-up at Lehigh University in the group of Professor David Moore, mass-selected Cu anions were co-deposited with krypton cations, leading to the successful detection of Cu atoms via UV/Vis absorption spectroscopy. Given the extremely low vapor pressure of Cu, those experiments served as a proof-of-principle for deposition of mass-selected ions, and led a later minimization of Cu-- neutralization in the matrix. |
