Edward A. Earl

ESR and ab initio theoretical studies of the cation radicals 14N+4 and 15N+4: The trapping of ion–neutral reaction products in neon matrices at 4 K

The 14N+4 and 15N+4 molecular cation radicals have been generated by the ion–neutral reaction N+2 +N2 and isolated in solid neon matrices at 4 K for detailed ESR (electron spin resonance) investigation. Both photonionization at 16.8 eV and electron bombardment (50 eV) were used in conjunction with the neon matrix trapping technique to produce the N+4 dimer cation. The ESR results clearly show that N+4 is linear and has a 2Σμ ground electronic state. The magnetic parameters in neon are: g∥=2.0016(4) and g⊥=1.9998(2); A∥(14N)=311(1) MHz and A⊥(14N)=264(1) MHz for the central atoms and ‖A∥‖=10.4(5) MHz and ‖A⊥‖=20.4(1) MHz for the outer or terminal 14N atoms. Electronic structure information for N+4 was obtained from the ESR results and compared with ab initio CI calculations. The unpaired electron resides primarily on the inner nitrogen atoms with significant 2pσ and 2s character. Orbital characters obtained from the commonly applied free atom comparison method (FACM) were compared with the results of a Mul...

Electron spin resonance investigations of 11B12C, 11B13C, and 10B12C in neon, argon, and krypton matrices at 4 K: Comparison with theoretical results

The first spectroscopic study of the diatomic radical BC is reported which confirms previous theoretical predictions of a 4∑− electronic ground state. The nuclear hyperfine interactions (A tensors) obtained for 11B, 10B, and 13C from the electron spin resonance (ESR) measurements are compared with extensive ab initio CI calculations. The BC molecule is one of the first examples of a small high spin radical for such an in‐depth experimental–theoretical comparison. The electronic structure of BC obtained from an analysis of the nuclear hyperfine interaction (hfi) is compared to that obtained from a Mulliken‐type population analysis conducted on a CI wave function which yields Aiso and Adip results in good agreement with the observed values. The BC radical was generated by the laser vaporization of a boron–carbon mixture and trapped in neon, argon, and krypton matrices at 4 K for a complete ESR characterization. The magnetic parameters (MHz) obtained for 11B13C in solid neon are: g∥ =2.0015(3); g⊥ =2.0020(3)...

Neon matrix ESR investigation of 12C+2 and 13C+2 : Confirmation of a 4Σ−g ground electronic state

The 12C+2 and 13C+2 cation radicals have been isolated in neon matrices by the photoionization of C2(g) generated by the laser vaporization of thin carbon disks. A new procedure of supporting and thermally outgassing such targets for laser vaporization ESR studies in rare gas matrices is described. The ESR results confirm the 4Σ−g ground electronic state assignment for C+2 and provide a valence orbital electronic structure characterization based on the 13C hyperfine structure (hfs). The ESR lines are extremely narrow for a high‐spin powder sample and an intense off‐angle or ‘‘extra’’ absorption feature exibits unusual hfs. Normally forbidden (ΔMS>1) transitions were detected at low magnetic fields. The magnetic parameters for 13C+2 in a neon matrix at 4 K are: D=3668(3) MHz; g⊥ =2.0018(5); g∥ =2.0023(5); ‖A∥‖ =99.4(8) MHz; and ‖A⊥‖ =95.2(5) MHz.

An ESR investigation of the F−2 radical anion in neon matrices at 4 K

The anion radical F−2 has been generated and trapped as a free ion in dilute neon matrices near 4 K and investigated by electron spin resonance (ESR). The magnetic parameters obtained in neon are: g∥ =2.0018(3); g⊥ =2.0185(3); A∥ =913.5(4), and A⊥ =−22.5(4) G. The neon ESR measurements are the first gas‐like results and these are compared with earlier findings for F−2 in various crystalline environments. Analysis of the combined results reveal that F−2 is the most gas‐like or least perturbed in the larger ionic lattices. The information obtained should be useful in estimating the degree of perturbation that typically exists for the many radicals which have been studied in ionic crystalline environments. Based upon these experimental findings for F−2 in neon matrices, an atomic value of Adip for a fluorine atom is proposed for estimating P orbital spin densities in ionic fluorine compounds. This experimental Adip for 19F is compared to commonly used theoretical values.

Reinvestigation of the aluminum hydride (AlH+ and AlD+) cation radicals by ESR in argon matrices at 4 K: Generation by reactive laser sputtering

The ESR spectra previously assigned to the AlH+ radical ion (X 2Σ) [J. Chem. Phys. 71, 3991 (1979)] actually belong to the divalent neutral aluminum radical AlHOH whose charge distribution and electronic structure can be described as AlH+OH− with 90% of the unpaired electron on the AlH+ part of the molecule. Reactive laser sputtering and photoionization of AlH(g) were used to generate the AlH+ and AlD+ cation radicals, whose ESR spectra have been observed for the first time. A detailed analysis of the ESR results for argon matrices at 4 K reveal unusually large Al hyperfine interaction (hfi) with Aiso and Adip values of 1586(2) and 49(1) MHz, respectively. The H hfi is essentially isotropic with Aiso=442(2) MHz. The observed nuclear hyperfine A tensors for Al and H show excellent agreement with ab initio CI theoretical calculations. The results for AlH+ are compared with the isoelectronic neutral radical MgH, and the similar AlF+ cation radical. The Al hfi is slightly larger in AlD+ relative to AlH+. This interesting isotopic effect is qualitatively explained on the basis of electronic structure dependence on small changes in the bond distance for the two isotopic radicals.The ESR spectra previously assigned to the AlH+ radical ion (X 2Σ) [J. Chem. Phys. 71, 3991 (1979)] actually belong to the divalent neutral aluminum radical AlHOH whose charge distribution and electronic structure can be described as AlH+OH− with 90% of the unpaired electron on the AlH+ part of the molecule. Reactive laser sputtering and photoionization of AlH(g) were used to generate the AlH+ and AlD+ cation radicals, whose ESR spectra have been observed for the first time. A detailed analysis of the ESR results for argon matrices at 4 K reveal unusually large Al hyperfine interaction (hfi) with Aiso and Adip values of 1586(2) and 49(1) MHz, respectively. The H hfi is essentially isotropic with Aiso=442(2) MHz. The observed nuclear hyperfine A tensors for Al and H show excellent agreement with ab initio CI theoretical calculations. The results for AlH+ are compared with the isoelectronic neutral radical MgH, and the similar AlF+ cation radical. The Al hfi is slightly larger in AlD+ relative to AlH+. This...

Neon matrix ESR and CI theoretical investigation of 10BF+ and 11BF+: Photoionization of BF from reactive laser sputtering and high temperature sources

The 11BF+ and 10BF+ radical cations have been generated and trapped in neon matrices at 4 K using the combined techniques of pulsed reactive laser sputtering and photoionization at 16.8 eV. An independent high temperature source of BF(g) in conjunction with photoionization was also employed and a comparison between these two different generation methods reveals no significant differences in their ESR spectra. The magnetic parameters for 11BF+ measured in neon matrices are g∥=2.0012(3), g⊥=2.0004(3), (11B) A∥=1784(1), and A⊥=1727(1) MHz, (19F)A∥=410(1), and A⊥=152(1) MHz. Extensive ab initio theoretical calculations have been conducted for BF+ and the nuclear hyperfine properties obtained from various types of CI wave functions show excellent agreement with the experimental measurements. Valence orbital occupancies obtained from a Mulliken‐type population analysis performed on the CI wave functions are compared with the conventional free atom comparison method for obtaining electronic structure information...

An electron spin resonance investigation of the 12C11B12C, 12C11B13C, and 13C11B13C radicals in neon, argon, and krypton matrices: Comparison with ab initio calculations

The 11 electron CBC radical has been generated by the pulsed laser vaporization of elemental carbon–boron mixtures and trapped in neon, argon and krypton matrices for detailed electron spin resonance (ESR) studies. Extensive comparisons of the experimental nuclear hyperfine A tenors for carbon and boron were made with a variety of ab initio computational results that involved different levels of theory and basis sets. These new ESR results agree with recent vibrational studies of CBC that show it to have a nonlinear symmetric geometry with a 2A1 electronic ground state. These ESR results provide a description of the singly occupied molecular orbital. The spin density resides primarily on boron in 2s and 2pz orbitals, however a complete resolution of the 13C hyperfine structure does show that approximately 20% resides on the carbon atoms.

The B3Li molecule's electronic and geometrical structure

The geometries, electronic energies, dipole moments, and local harmonic vibrational frequencies of the singlet ground and low‐energy singlet valence excited states of B3Li have been investigated using (i) correlation‐consistent double‐zeta plus polarization basis sets, (ii) small valence‐space complete active space multiconfiguration self‐consistent field electronic wave functions, and (iii) analytical energy derivative techniques combined with automated potential energy surface ‘‘walking’’ algorithms. The lowest‐energy structure of B3Li is found to have C3v symmetry and to consist of a Li atom that sits above the center of an equilateral B3 moiety; the dipole moment of this species is 6.7 D and its dissociation energy (not zero point corrected) to ground state B3+Li is 60 kcal/mol. The B3H analog of this C3v structure is not a geometrically stable species for reasons that are analyzed here. A second stable structure (with dipole moment of 8.5 D and dissociation energy of 47 kcal/mol) is planar and has th...