Jon D. Langenberg

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...

Dispersed fluorescence spectroscopy of jet-cooled AgAu and Pt2

Dispersed fluorescence spectroscopy has been used to study jet-cooled AgAu and Pt2. Fluorescence resulting from the excitation of five bands of the A←X 1Σ+ system of AgAu was dispersed, and 51 measured ground state vibrational levels were fit to provide ground state vibrational constants of ωe″=198.22±0.11 cm−1 and ωe″xe″=0.512±0.002 cm−1. A Franck–Condon calculation was performed using the experimental values of the ground and excited state vibrational frequencies and anharmonicities, providing an estimate of the change in bond length upon excitation of the A←X system of Δre=0.214±0.005 A. Fluorescence resulting from four different excitations of Pt2 was dispersed, providing vibrational constants for the ground and two low-lying excited states. Ground state vibrational constants of ωe=222.3 cm−1 and ωexe=0.62 cm−1 were obtained, based on the analysis of 16 measured ground state vibrational levels. In addition, a low-lying excited state was located at T0=2877 cm−1, with ωe=197 cm−1. This state perturbed t...

Resonant two-photon ionization spectroscopy of jet-cooled RuC

A resonant two-photon ionization study of the jet-cooled RuC molecule has identified the ground state as a 1Σ+ state arising from the 10σ211σ25π42δ4 configuration. The 3Δi state arising from the 10σ211σ25π42δ312σ1 configuration lies very low in energy, with the 3Δ3 and 3Δ2 components lying only 76 and 850 cm−1 above the ground state, respectively. Transitions from the X 1Σ+, 3Δ3, and 3Δ2 states to the 3Π2, 3Π1, 3Φ3, 3Φ4, 1Φ3, and 1Π1 states arising from the 10σ211σ25π42δ36π1 configuration have been observed in the 12 700–18 100 cm−1 range, allowing all of these states to be placed on a common energy scale. The bond length increases as the molecule is electronically excited, from r0=1.608 A in the 2δ4, X 1Σ+ state, to 1.635 A in the 2δ312σ1, 3Δ state, to 1.66 A in the 2δ36π1, 3Π and 3Φ states, to 1.667 A in the 2δ36π1, 1Φ and 1.678 A in the 2δ36π1, 1Π state. A related decrease in vibrational frequency with electronic excitation is also observed. Hyperfine splitting is observed in the 2δ312σ1, 3Δ3 state for...

Resonant two-photon ionization spectroscopy of jet-cooled PdC

The first optical investigation of the spectra of diatomic PdC has revealed that the ground state has Ω=0+, with a bond length of r0=1.712 A. The Hund’s case (a) nature of this state could not be unambiguously determined from the experimental data, but dispersed fluorescence studies to be reported in a separate publication, in combination with a comparison to theoretical calculations, demonstrate that it is the 2δ4 12σ2, 1Σ0++ state, which undergoes spin–orbit mixing with a low-lying 2δ4 12σ1 6π1, 3Π0+ state. An excited 3Σ+ state with re=1.754±0.003 A (r0=1.758±0.002 A) and ΔG1/2=794 cm−1 is found at T0=17 867 cm−1. Although only the Ω=1 component of this state is directly observed, the large hyperfine splitting of this state for the 105Pd 12C isotopomer implies that an unpaired electron occupies an orbital that is primarily of 5s character on Pd. Comparison to ab initio calculations identifies this state as 2δ4 12σ1 13σ1, 3Σ1+. To higher wavenumbers a number of transitions to states with Ω=0+ have been o...

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.

Resonant two-photon ionization spectroscopy of jet-cooled PtSi

Jet-cooled diatomic PtSi, produced in a laser ablation supersonic expansion source, has been spectroscopically investigated between 17 400 and 24 000 cm−1 by resonant two-photon ionization spectroscopy. Two vibrational progressions are observed and identified as the [15.7]Ω′=1←X 1Σ+ and [18.5]Ω′=1←X 1Σ+ band systems. Three bands in the former system and six bands in the latter system were rotationally resolved and analyzed, leading to bond lengths of re′=2.1905(13) A and re′=2.2354(3) A for the [15.7]Ω′=1 and [18.5]Ω′=1 states, respectively. The Ω″=0 ground state of PtSi is assigned as a 1Σ+ state, in agreement with previous work and with the assigned ground states of the isovalent NiC, PdC, PtC, and NiSi molecules. The ground state bond length of PtSi is given by r0″=2.0629(2) A. A Rydberg–Klein–Rees analysis of the ground and excited state potential energy curves is presented, along with a discussion of the chemical bonding and a comparison to the isoelectronic molecule, AlAu. Evidence is presented for ...

The bond energy of Rh2

In a spectroscopic investigation of jet-cooled Rh2 by the resonant two-photon ionization method, an abrupt predissociation threshold is observed in a dense set of vibronic levels at 19 405±4 cm−1. Based on the high density of states expected in the rhodium dimer, the sharp definition of the predissociation threshold that is observed, and the validation of a similar conclusion in the case of V2, it is argued that predissociation occurs as soon as the energy of the separated ground state atoms is exceeded. On this basis the bond energy of Rh2 is assigned as D0(Rh2)=19 405±4 cm−1=2.4059±0.0005 eV. This value is compared to the results of other experiments and to theoretical calculations. The bond energy of disilver, D0(Ag2)=1.65±0.03 eV, provides a particularly useful standard of comparison, and suggests that 4d contributions to the bond energy of Rh2 amount to at least 0.76 eV.

Bond energies of transition metal dimers: TiZr, TiNb, and ZrV

Abstract The bond dissociation energies of TiZr, TiNb, and ZrV have been determined by the abrupt onset of predissociation in an extremely congested vibronic spectrum of these molecules. From these predissociation thresholds the dissociation energies are determined to be D 0 (TiZr) = 2.183 ± 0.001 eV, D 0 (TiNb) = 3.092 ± 0.001 eV, and D 0 (ZrV) = 2.663 ± 0.003 eV. After making a correction for the promotion energies required to prepare the atoms for bonding, the intrinsic bond energies of these molecules are compared and periodic trends in the bonding of the 3d-4d mixed transition metal dimers are discussed.

Dispersed fluorescence spectroscopy of AlNi, NiAu, and PtCu

Dispersed fluorescence studies of AlNi, NiAu, and PtCu have been performed, providing spectroscopic information about the ground and low-lying excited electronic states. Vibrational frequencies are reported for the ground X 2Δ5/2 state of all three molecules. In the case of AlNi, fluorescence to all five of the states originating from the 3dNi93sAl2σ2 manifold has been observed. For both NiAu and PtCu, fluorescence to two low-lying excited states in addition to the ground state was observed. Relative energies, vibrational constants, and, when possible, Ω values of these states are reported. Comparisons of the measured electronic states to the predictions of a ligand-field plus spin–orbit model are also provided, along with a comparison of the electronic structure of PtCu to that of PtH.

Spectroscopy of jet-cooled Ag2Au

Abstract Resonant two-photon ionization spectroscopy has been used to study the supersonically cooled metal cluster, Ag 2 Au. One electronic band system has been observed, with the origin band at 17525 cm −1 . Vibronic progressions have been found and analyzed using a least-squares fitting procedure. The molecule is assigned as belonging to the C 2v point group in both the ground and the excited eletronic states, and vibrational progressions in both of the two totally symmetric (a 1 ) vibrational modes have been identified, giving values of ω′ 1 = 200.15 ± 0.49 cm −1 and ω′ 2 = 111.28 ± 0.62 cm −1 for the excited electronic state of the 107 Ag 109 Ag 197 Au isotopic modification. Anharmonicities x ′ 11 , x ′ 12 , and x ′ 22 are also reported for the excited electronic state, along with lifetime measurements for several vibronic levels. This work also places the ionization potential of Ag 2 Au in the range 5.00 ⩽ IP (Ag 2 Au) ⩽ 6.42 eV.