Caleb A. Arrington

Ni2 revisited: Reassignment of the ground electronic state

Resonant two‐photon ionization spectroscopy was used to study jet‐cooled Ni2 produced by pulsed laser ablation of a nickel target in the throat of a supersonic nozzle using argon as the carrier gas. Spectral regions previously investigated using helium as the carrier gas were reinvestigated, and the improved cooling achieved was found to suppress transitions arising from an Ω=4 state that had been thought to be the ground state. Seven new vibronic progressions were assigned, with spectroscopic constants determined for the excited states. The predissociation threshold in Ni2 was reinvestigated, and a revised value for the binding energy is given as D○0(Ni2)=2.042±0.002 eV. The ionization energy of Ni2 was found to be 7.430±0.025 eV, and from this result and the revised bond dissociation energy of the neutral, the binding energy of the cation was calculated to be D○0(Ni+2)=2.245±0.025 eV. Similarly, D○0(Ni−2)=1.812±0.014 eV is obtained using D○0(Ni2) and the electron affinities of Ni and Ni2. Twenty bands w...

The 3Π0u ← X 3Δ1g band system of jet‐cooled Ti2

A band of jet‐cooled 48Ti2 has been located in the near infrared by resonant two‐photon ionization spectroscopy. Rotational analysis has shown the band to be an Ω’=0±←Ω‘=1 transition, which is consistent with the 3Δg ground state proposed by Bauschlicher et al. [J. Chem. Phys. 95, 1057 (1991)]. The band is assigned as a 3Π0u ← X 3Δ1g transition, and lower and upper state bond lengths have been determined as r0(X 3Δg)=1.9422±0.0008 A and r0(3Πu)=1.997±0.009 A (1σ error limits, corrected for spin–uncoupling effects). Comparisons are made to the TiV and V2 molecules, a rationale for the unusual filling order of the 3d‐based molecular orbitals is provided, and molecular orbital assignments are considered for the excited 3Πu state.

Spectroscopic studies of jet‐cooled AlNi

Resonant two‐photon ionization spectroscopy has been applied to jet‐cooled diatomic CuAg. Four band systems have been observed, three of which have been rotationally resolved and analyzed. The ground state is X 1Σ+ in symmetry, deriving from the 3d10Cu4d10Agσ2 molecular configuration. Its bond length has been determined as r0=2.3735±0.0006 A (1σ error limits). Based on an analysis of the possible separated atom limits, three of the excited states observed (A 0+, A’ 1, and B’ 0+ ) are assigned as primarily 3d9Cu4d10Agσ2σ* in character. The observation of unusually large electronic isotope shifts in the A–X, A’–X, and B’–X band systems, similar in magnitude to those previously observed in the A–X and B–X systems of Cu2 and the s←d excitations in atomic copper, provides further confirmation that these excited states derive from the 3d9Cu4d10Agσ2σ* molecular configuration. Finally, the highest energy state observed in this work is argued to be primarily ion pair in character, and is expected to have significa...

Spectroscopic analysis of jet‐cooled AlCu

Diatomic AlCu has been interrogated using resonant two‐photon ionization spectroscopy in a supersonic expansion of helium. The ground state is shown to be X 1Σ+, deriving from the 3sAl23dCu10σ2 configuration, in agreement with theoretical predictions. The closed‐shell nature of this molecule results in a low density of electronic states, allowing the chemical bonding and electronic structure to be investigated in detail. Five excited electronic states have been observed and characterized, leading to a potential energy diagram based solely on experimental results. Constants experimentally determined for AlCu include a ground state bond length (r0) of 2.3389±0.0004 A, a dissociation energy, D0○, of 2.315±0.012 eV, and an ionization potential of 7.065±0.014 eV.

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(...

Resonant two‐photon ionization spectroscopy of coinage metal trimers: Cu2Ag, Cu2Au, and CuAgAu

The jet‐cooled coinage metal triatomic molecules Cu2Ag, Cu2Au, and CuAgAu have been investigated using resonant two‐photon ionization spectroscopy. One band system, labeled as the A–X system, has been observed for each species, with origin bands at 13 188, 17 217, and 17 470 cm−1, respectively. Vibrational progressions have been assigned and vibrational constants have been extracted using a linear least‐squares fitting procedure. For Cu2Ag, 47 vibrational bands have been assigned within the A–X system. The upper states of these bands derive from combinations of two symmetric (a1) and one antisymmetric (b2) mode in the C2v point group. For the A–X system of Cu2Au, only seven vibrational bands have been observed, all occurring within a 500 cm−1 range. Lifetime measurements for the observed vibrational levels support the possibility that predissociation may be occurring in the A excited state of Cu2Au and this may be limiting the number of vibrational levels observed within this state. Finally, in the...

Spectroscopy of mixed early–late transition metal diatomics: ScNi, YPd, and ZrCo

Resonant two‐photon ionization spectroscopy has been employed to investigate the spectra of the jet‐cooled transition metal diatomics ScNi, YPd, and ZrCo, which are isovalent species which possess (or are thought to possess) an X 2Σ+ ground state. Several electronic band systems have been observed for these species in the near infrared, and the analysis of these systems is reported. Ground state vibrational intervals of ΔG1/2‘ = 334.5 ± 1.0, 264.4±0.2, and 357.7 cm−1 have been determined for ScNi, YPd, and ZrCo, respectively. The spectroscopic results obtained for ScNi and YPd are compared to theoretical calculations performed by other researchers, and a discussion of the chemical bonding in these species is presented.

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...

Spectroscopy of jet-cooled YCu

Optical spectra of jet‐cooled diatomic YCu have been recorded using resonant two‐photon ionization spectroscopy in a supersonic expansion of helium. The ground state is shown experimentally to be of 1Σ+ symmetry, with a measured bond length of re‘=2.6197(6) A and a vibrational frequency of 193.21(24) cm−1 for 89Y63Cu. Five excited electronic states are identified as the [10.2]1Σ+ state, the [11.8]3Π0+ state, the [12.0]3Π1 state, the [14.0]1Π state, and, with the help of ab initio theory, the [12.2]1Π state. No evidence whatever for participation of the 3d orbitals of copper in the chemical bonding is found, and the electronic structure of YCu is found to exhibit a striking similarity to that of YH.