Robert M. Babb

Electron spin resonance matrix isolation and ab initio theoretical investigations of 69,71GaH2, 69,71GaD2, H69,71GaCH3, and D69,71GaCD3

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 hyperfine interactions. A comparison with similar radicals is presented, including BH2, AlH2, HAlCH3, HAlOH, and AlH+.

Laser vaporization generation of the SiB and SiAl radicals for matrix isolation electron spin resonance studies; comparison with theoretical calculations and assignment of their electronic ground states as X 4Σ

The first experimental spectroscopic study of the SiB and SiAl diatomic radicals is reported. Electron spin resonance results indicate that both molecules have X 4Σ ground electronic states, in agreement with earlier theoretical calculations. The SiB and SiAl radicals were generated in neon matrices at 4 K by trapping the products produced from the pulsed laser vaporization of their alloys. Electronic structure information for these radicals is especially interesting given the utilization of silicon doped materials in semiconductor applications. The observed nuclear hyperfine interactions (A tensors) for 10B, 11B, and 27Al in these molecular radicals were compared with the results of ab initio configuration‐interaction theoretical calculations which were conducted as part of this experimental study. The neon matrix magnetic parameters (MHz) for Si 11B are D=800(2), g∥=2.0014(8), g⊥=2.0005(4), A⊥=92.4(5), and A∥=111(2). For Si 27Al the results (MHz) are D=9710(2), g∥=1.9994(8), and g⊥=1.9978(4), ‖A⊥‖=10.3(...

Electron spin resonance investigation of Sc+2 in neon matrices and assignment of its ground electronic state as X 4Σ−. Comparison with theoretical calculations

The discandium radical cation, Sc+2, has been isolated in neon matrices at 4 K and studied by electron spin resonance (ESR) spectroscopy and theoretical methods. It was produced by the x‐irradiation of neon matrix samples containing neutral Sc2 which was formed by trapping the products generated from the pulsed laser vaporization of scandium metal. The experimental and theoretical findings indicate that Sc+2 has a 4Σ−g electronic ground state compared to an X 5Σ−u state for the neutral discandium radical. The large decrease in the 45Sc hyperfine interaction (A tensor) going from Sc2 to Sc+2 provides direct experimental information concerning the types of valence molecular orbitals that are involved in these diatomic radicals. The neon matrix magnetic parameters for 45Sc+2 are g∥≊2.00, g⊥=1.960(1), ‖A∥‖=28(6), and ‖A⊥‖=26.1(3) MHz; the D value (zero field splitting) was 15 381(3) MHz. Ab initio configuration interaction (CI) calculations of the nuclear hyperfine interactions yielded results in reasonable a...

Electron spin resonance and theoretical studies of the PO2 and AsO2 radicals in neon matrices at 4 K: Laser vaporization and x‐irradiation radical generation techniques

The utilization of high energy generation techniques for trapping ion radicals and other reactive intermediates in neon matrices at 4 K is discussed. Electron spin resonance (ESR) results for several small radicals are presented to demonstrate the application of x irradiation and reactive laser vaporization for neon matrix isolation studies. Detailed ESR studies of the PO2 and AsO2 radicals, along with ab initio theoretical computations of their nuclear hyperfine interactions, are presented. No previous ESR observations have been reported for these radicals, although PO2 has been studied under high resolution in the gas phase utilizing far‐infrared laser magnetic resonance and microwave spectroscopies.

Laser vaporization generation of the diatomic radicals PdB, 105PdB, PdAl, and 105PdAl: Electron spin resonance investigation in neon matrices at 4 K

The new diatomic radicals PdB and PdAl have been generated by depositing the products produced from the pulsed laser vaporization of the elemental mixtures into neon matrices at 4 K. ESR (electron spin resonance) studies of these matrix isolated radicals, including an analysis of the 105Pd(I=5/2), 27Al(I=5/2), and 11B(I=3/2) nuclear hyperfine interactions, show that both have X 2Σ electronic ground states. These new results are compared with previous ESR measurements for PdH, PdCH3, YPd, ScPd, and PdH2+ to reveal electronic structure information and bonding trends as the complexity of the ligand increases 1s, 2p, 3p, 3d, and 4d. Ab initio UHF (unrestricted Hartree–Fock) theoretical calculations were also conducted on four of these small palladium radicals as part of this experimental investigation. A simple interpretation of the 105Pd hyperfine interactions and molecular g tensors based on the degree of charge transfer to palladium is presented. The observed magnetic parameters (MHz) for 105Pd11B in a neo...

Electron spin resonance rare gas matrix studies of 12CO2−, 13CO2−, and C17O−2: Comparison with ab initio calculations

The 12C16O2−, 13C16O2−, 12C17O2−, and 12C16,17O2− radical anions have been generated by four independent methods and isolated in neon and argon matrices for detailed ESR (electron spin resonance) investigations. Included with these experimental measurements for the various magnetic parameters of CO−2 are high level ab initio calculations (MR SD‐CI and others) of the 13C and 17O hyperfine A tensors. Some of the calculations included the effects of a 42‐atom neon cage on the electronic structure of CO−2. Previous ESR studies of CO−2 have been conducted in more perturbing environments, such as ionic crystals, where the close proximity of the counter cation can alter the anion’s properties. A comparison of the earlier measurements in more interactive materials with these theoretical and rare gas matrix results reveals a significantly different distribution of the spin density. The neon magnetic parameters (MHz) for CO−2 are gx=2.0018, gy=1.9964, gz=2.0010; for 13C, Ax=320.4, Ay=296.1, Az=394.5; for 17O, Ax=−8...

Laser vaporization generation of Y 10B+, Y 11B+, and YAl+ for electron spin resonance studies in neon matrices at 4 K: Comparison with theoretical calculations

The first spectroscopic investigation of 89Y 10B+, 89Y 11B+, and 89Y 27Al+ is reported, revealing that both of these diatomic cation radicals have X 4Σ− electronic ground states. The ions were generated by three high energy techniques in combination with neon matrix isolation at 4 K and studied by electron spin resonance (ESR) spectroscopy. The generation methods included pulsed laser vaporization of the metal alloys, photoionization at 16.8 eV during matrix deposition, and x‐irradiation at 80 keV of the matrix sample following deposition. Hyperfine interactions were resolved for all of the above nuclei and were compared with calculated isotropic and dipolar components of the A tensor. The yttrium 5s character observed in YAl+ was significantly larger than that in YB+ based upon the observed nuclear hyperfine interactions. The calculated electronic structure properties showed agreement with this trend in the observed Aiso parameters. In addition, qualitative descriptions of the bonding properties are also...

Neon and argon matrix ESR and theoretical studies of the 12CH3Cd,12CD3Cd, 13CH3Cd, 12CH3111Cd, and 12CH3113Cd radicals

Electron spin resonance (ESR) studies are reported for the first time on the various isotopomers of the CH3Cd radical isolated in neon and argon matrices. The radicals were generated in neon matrices by the reaction of laser-ablated cadmium metal and various methyl precursors, and in argon matrices by x-irradiation. The neon matrix values measured were g⊥=1.9491(1), A⊥(H)=17.0(1) MHz, A⊥(D)=2.6(1) MHz, A⊥(13C)=163(3) MHz, and A⊥(111Cd)=−3083(3) MHz, and estimates were derived for A∥(13C)=230(50) MHz and A∥(111Cd)=−3486(5) MHz. The argon matrix values measured were g⊥=1.952(1), A⊥(H)=16(1) MHz and A⊥(111Cd)=−3301(3) MHz, and an estimate was derived for A∥(111Cd)=−3704(5) MHz. The ESR experimental Adip(111Cd) values for the neon and the argon matrices agree with the reported gas-phase value [J. Chem. Phys. 101, 6396 (1994)]. The matrix ESR Aiso(111Cd) values show small shifts compared with the gas-phase results (5% greater for the neon matrix and 12% greater for the argon matrix). At 4.3 K in the neon matri...

Electron‐spin resonance studies of the titanium cation (Ti+,3d3,4F) in rare gas matrices at 4 K: A crystal field interpretation

Electron‐spin resonance studies of laser‐ablated titanium metal isolated in neon and argon display an intense feature which exhibits a symmetric, narrow line and a large matrix‐dependent g shift. On the basis of a number of experiments, this is assigned to a matrix isolated 3d3,4F Ti+ ion in an octahedral matrix environment. Although the ground state of the gas‐phase Ti+ ion is 3d24s1,4F, the assignment to the 3d3,4F state is supported by the small hyperfine structure which is observed. The neon magnetic parameters are: g=1.934(1) and A(47Ti)=64(1) MHz; for argon, g=1.972(1) and A=56(1) MHz. This unusual stabilization of an excited atomic state by a rare gas matrix is consistent with ab initio studies, and has been previously found for atomic nickel. A crystal‐field study of the expected behavior of a d3,4F ion isolated in a tetrahedral, octahedral, or cuboctahedral environment supports the assignment to an octahedral Ti+(Rg)6 species, and using the atomic spin–orbit parameter, ζ permits accurate values o...