ELECTRON SPIN RESONANCE INVESTIGATION OF FORMATION MECHANISMS OF MATRIX ISOLATED H4+H_{4}^{+}

Author Institution: Department of Chemistry, Furman University, Greenville, SCHydrogen cluster ions are of interest as reactants in astrophysical processes and as simple models for theoretical calculations. In this work, the formation mechanism of $H_{4}^{+}$ and its deuterated isotopomers was investigated by varying the experimental conditions required to observe $H_{4}^{+}$ isolated in a neon matrix. The $H_{4}^{+}$ cluster was formed by mixing $H_{2}$, $D_{2}$, and HD gases with neon and depositing the mixtures onto a copper rod cooled by liquid helium. The resulting matrix was then x-irradiated at 60 keV for 30 minutes and electron spin resonance spectra were recorded. Previous studies conducted in our lab have indicated that hydrogen cluster cations can only be formed at extremely low temperatures (2.6 K) and are very sensitive to temperature change. In the current study, the local environment of the deposition region was characterized by investigating the allowable temperature range, the effect of sample gas flow rate, and the need for nearby cold surfaces

Vibrational and Electronic Absorption Spectroscopy of 2,3-Benzofluorene and Its Cation

Benzofluorene (C17H12) has been studied in argon matrices via Fourier transform infrared and UV?visible absorption spectroscopy. The analysis of the infrared absorption spectra of neutral and cationic 2,3-benzofluorene was supported by density functional theory (DFT) B3LYP/6-311+G** calculations of the harmonic-mode frequencies. Extensive time-dependent DFT calculations of the electronic vertical excitation energies with BLYP/6-31++G** and B3LYP/6-31++G** functionals/basis sets and the Casida?Salahub asymptotic correction were performed to assign the observed electronic absorption bands of the neutral species. Although the observed low-energy absorption bands are predicted well by theory, the higher-energy bands (Sn ? S0 transitions, n ≥ 4) have been assigned only tentatively. However, the observed electronic absorption bands for the parent, singly dehydrogenated cationic and neutral species are in accord with TDDFT (BLYP/6-31G**) results. The possibility that the 2,3-benzofluorene cation contributes to the unidentified infrared (UIR) bands observed from interstellar space is discussed briefly. Benzofluorene (C17H12) has been studied in argon matrices via Fourier transform infrared and UV?visible absorption spectroscopy. The analysis of the infrared absorption spectra of neutral and cationic 2,3-benzofluorene was supported by density functional theory (DFT) B3LYP/6-311+G** calculations of the harmonic-mode frequencies. Extensive time-dependent DFT calculations of the electronic vertical excitation energies with BLYP/6-31++G** and B3LYP/6-31++G** functionals/basis sets and the Casida?Salahub asymptotic correction were performed to assign the observed electronic absorption bands of the neutral species. Although the observed low-energy absorption bands are predicted well by theory, the higher-energy bands (Sn ? S0 transitions, n ≥ 4) have been assigned only tentatively. However, the observed electronic absorption bands for the parent, singly dehydrogenated cationic and neutral species are in accord with TDDFT (BLYP/6-31G**) results. The possibility that the 2,3-benzofluorene cation contributes to the unidentified infrared (UIR) bands observed from interstellar space is discussed briefly

Vibrational and electronic spectroscopy of acenaphthylene and its cation

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ELECTRON SPIN RESONANCE INVESTIGATION OF MASS-SELECTED, MATRIX ISOLATED RADICAL CATIONS

Author Institution: Department of Chemistry, Furman University, Greenville, SC 29613Small mass-selected, radical cations were matrix isolated and investigated by ESR spectroscopy. Ions produced by electron bombardment were mass-selected in a quadrupole filter and co-deposited with neon on a 4 K copper surface. The unit resolution of the quadrupole mass filter enabled distinction of adjacent ions in the mass spectrum. Collisional fragmentation of selected ions was minimized by low ion energies (15-30 eV). Ion beam current ranged from 0.2 nA to 2 nA. During deposition, the matrix was neutralized by an electron beam perpendicular to the ion flow. Because positive and negative species were trapped in separate matrix sites, matrix neutrality was maintained without total cation elimination. Systems studied include various boron hydride cations, hydrocarbon cations of astrophysical interest, and the first observation of matrix isolated $^{16}$O$^{+}$ and $^{17}$O$^{+}$

ELECTRON SPIN RESONANCE INVESTIGATIONS OF MATRIX ISOLATED METAL CLUSTERS AT 4 K

Author Institution: Department of Chemistry, Furman University, Greenville, SC 29613High-spin magnesium and calcium neutral clusters and zinc cluster radical cations were isolated in neon matrices at 4 K and studied by ESR spectroscopy. Solid magnesium, calcium, and zinc were vaporized in a resistively heated tantalum Knudsen cell and co-deposited with neon or argon on a copper flat at 4 K. High-spin neutral metal clusters were observed for both magnesium ($^{3}{\Sigma}$) and calcium ($^{5}{\Sigma}$). Experimental values for the fine structure interactions (D-tensor) were determined by fitting the observed fine structure lines to those obtained from an exact diagonalization of the spin Hamiltonian. Due to the large proportion of p-orbital contribution, no hyperfine interactions were resolved. In these experiments, zinc cluster cation radicals were also generated by X-irradiation of matrix isolated zinc clusters. Experimental values of the nuclear hyperfine interactions (A-tensor) for $^{67}$Zn$_{n}^{+}$ (n = 1-4) radicals were determined. Small shifts observed in g-values demonstrate some d-orbital contribution to cluster bonding

Photodissociation Pathways of the 2,3-Benzofluorene Cation

Benzofluorene (C17H12) cations have been studied in the vapor phase by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The identification of certain fragmented species from electron impact/matrix optical experiments (see Banisaukas, J.; Szczepanski, J.; Vala, M.; Hirata, S. J. Phys. Chem. A 2004, 108, 3713) provided the background for the present detailed studies of the dissociation pathways of the cation via FT-ICR mass spectrometry. Both hydrogen and acetylene loss pathways along various photodissociation routes have been identified. Benzofluorene (C17H12) cations have been studied in the vapor phase by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The identification of certain fragmented species from electron impact/matrix optical experiments (see Banisaukas, J.; Szczepanski, J.; Vala, M.; Hirata, S. J. Phys. Chem. A 2004, 108, 3713) provided the background for the present detailed studies of the dissociation pathways of the cation via FT-ICR mass spectrometry. Both hydrogen and acetylene loss pathways along various photodissociation routes have been identified

MATRIX ISOLATION ELECTRON SPIN RESONANCE INVESTIGATION OF H2_2+^+, H4_4+^+, AND THEIR ISOTOPOMERS

Author Institution: Department of Chemistry, Furman University, Greenville, S.C. 29613Hydrogen cluster ions are of interest as reactants in astrophysical processes and as simple models for theoretical calculations. In this work, H$_4$$^+$ and its deuterated isotopomers were isolated in a neon matrix and investigated by electron spin resonance spectroscopy. The various isotopomers were formed by mixing H$_2$, D$_2$, and HD gases with neon and depositing the mixtures onto a copper rod cooled to 2.6 K. The matrices were then x-irradiated at 60 keV for 30 minutes. Electron spin resonance spectra were recorded for H$_4$$^+$, H$_3$D$^+$, H$_2$D$_2$$^+$, HD$_3$$^+$, and D$_4$$^+$ at temperatures ranging from 2.6 K to 9 K. These isotopomers could only be formed at 2.6 K, and were very sensitive to changes in temperature. Diatomic hydrogen ions (H$_2$$^+$ and HD$^+$) were also observed at 2.6 K at low sample gas concentrations. Experimental values for the hyperfine interactions were determined by fitting the observed hyperfine structure lines with those obtained from an exact diagonalization of the spin Hamiltonian

Electron spin resonance matrix isolation and ab initio theoretical investigations of\u3csup\u3e69,71\u3c/sup\u3eGaH\u3csub\u3e2\u3c/sub\u3e, \u3csup\u3e69,71\u3c/sup\u3eGaD\u3csub\u3e2\u3c/sub\u3e, H\u3csup\u3e69,71\u3c/sup\u3eGaCH\u3csub\u3e3\u3c/sub\u3e, and \u3csup\u3eD69,71\u3c/sup\u3eGaCD\u3csub\u3e3\u3c/sub\u3e

First time electron spin resonance studies are reported for various isotopomers of GaH2 and HGaCH3. The radicals were generated in neon matrices at 4 K by the ultraviolet photoexcitation of Ga which undergoes insertion reactions with H2 and CH4. Ab initio calculations with a large uncontracted basis and configuration interaction with all single excitations from the spin-€restricted Hartree-Fock configuration gave good agreement with the experimental results and supported the free atom comparison method interpretation of the hyperfineinteractions. A comparison with similar radicals is presented, including BH2, AlH2, HAlCH3, HAlOH, and AlH+