Zero Electron Kinetic Energy Photoelectron Research Articles

Pulsed-field ionization zero electron kinetic energy spectrum of the ground electronic state of BeOBe+

The ground electronic state of BeOBe(+) was probed using the pulsed-field ionization zero electron kinetic energy photoelectron technique. Spectra were rotationally resolved and transitions to the zero-point level, the symmetric stretch fundamental and first two bending vibrational levels were observed. The rotational state symmetry selection rules confirm that the ground electronic state of the cation is (2)Σ(g)(+). Detachment of an electron from the HOMO of neutral BeOBe results in little change in the vibrational or rotational constants, indicating that this orbital is nonbonding in nature. The ionization energy of BeOBe [65480(4) cm(-1)] was refined over previous measurements. Results from recent theoretical calculations for BeOBe(+) (multireference configuration interaction) were found to be in good agreement with the experimental data.

Ab initio potentials for states of XeI, XeI − and XeI +

Results from high-level quantum chemical computations (coupled clusters [CCSD(T)] and multireference average coupled-pair functional [MR-ACPF], using relativistic effective core potential [ECP] basis sets) are presented for XeI, XeI − and XeI +. Comparison is made with published determinations of bond length, dissociation energy and vibrational parameters from atomic scattering, fluorescence, zero electron kinetic energy photoelectron spectroscopy experiments, and previous calculation. For the neutral molecule, MR-ACPF, including spin–orbit coupling, provides results for all six valence states. Overall, good agreement between calculated and experimental results is observed. Further, predictions for the harmonic vibrational frequency and anharmonicity of XeI +, a species which has not yet been observed in experiment, are given for the first time.

Benchmark calculations on the adiabatic ionization potentials of M–NH3 (M=Na,Al,Ga,In,Cu,Ag)

The ground states of the M-NH(3) (M=Na,Al,Ga,In,Cu,Ag) complexes and their cations have been studied with density functional theory and coupled cluster [CCSD(T)] methods. The adiabatic ionization potentials (AIPs) of these complexes are calculated, and these are compared to results from high-resolution zero-electron kinetic energy photoelectron spectroscopy. By extrapolating the CCSD(T) energies to the complete basis set (CBS) limit and including the core-valence, scalar relativistic, spin-orbit, and zero-point corrections, the CCSD(T) method is shown to be able to predict the AIPs of these complexes to better than 6 meV or 0.15 kcal/mol. 27 exchange-correlation functionals, including one in the local density approximation, 13 in the generalized gradient approximation (GGA), and 13 with hybrid GGAs, were benchmarked in the calculations of the AIPs. The B1B95, mPW1PW91, B98, B97-1, PBE1PBE, O3LYP, TPSSh, and HCTH93 functionals give an average error of 0.1 eV for all the complexes studied, with the B98 functional alone yielding a maximum error of 0.1 eV. In addition, the calculated metal-ammonia harmonic stretching frequencies with the CCSD(T) method are in excellent agreement with their experimental values, whereas the B3LYP method tends to underestimate these stretching frequencies. The metal-ammonia binding energies were also calculated at the CCSD(T)/CBS level, and are in excellent agreement with the available experimental values considering the error limits, except for Ag-NH(3) and Ag(+)-NH(3), where the calculations predict stronger bond energies than measured by about 4 kcal/mol, just outside the experimental error bars of +/-3 kcal/mol.

Pulsed-field ionization electron spectroscopy and conformation of copper-diammonia

Copper-diammonia, Cu(NH3)2, and its deuterated species, Cu(ND3)2, are produced in supersonic molecular beams and studied by pulsed-field ionization zero electron kinetic energy photoelectron spectroscopy and ab initio calculations. Structural isomers with a copper atom binding to an ammonia dimer or two ammonia molecules are obtained by the calculations. By comparing the experimental measurements to the theoretical calculations, the neutral and ionic forms of copper-diammonia are determined to be in a doubly bound linear conformation in their ground electronic states. The adiabatic ionization potentials of Cu(NH3)2 and Cu(ND3)2 are measured as 29,532 (5) and 29,313 (5) cm(-1), respectively. The metal-ligand symmetric stretching frequencies are measured to be 436 cm(-1) for Cu+-(NH3)2 and 398 cm(-1) for Cu+-(ND3)2, and the metal-ligand bending frequencies 75,139 cm(-1) for CuCu+-(NH3)2 and 70125 cm(-1) for CuCu+-(ND3)2. Moreover, the dissociation energy of Cu(NH3)2-->CuNH3+NH3 is determined to be 11(3) kcal mol(-1) through a thermodynamic relationship.

Zero electron kinetic energy photoelectron and threshold photoionization spectroscopy of M-X(CH3)3 (M = Ga, In; X = P, As)

This paper presents pulsed-field ionization, zero electron kinetic energy (ZEKE) photoelectron and threshold photoionization spectra of M-X(CH3)3 (M = Ga, In; X = P, As). The ZEKE spectra exhibit well-resolved vibrational structures. A comparison with B3LYP calculations shows that the spectrum of In-P(CH3)3 arises from the 1A1 ← 2E transition and the spectra of Ga-P(CH3)3 and Ga-As(CH3)3 arise from transitions of a Jahn–Teller distorted doublet state to the 1A1 state. The intensities of the 1A1–2E transition in the indium species are described with the Franck–Condon approximation, while the transitions in the gallium complexes are more complicated due to the dynamic Jahn–Teller effect. The adiabatic ionization potentials of Ga-P(CH3)3, In-P(CH3)3, and Ga-As(CH3)3 are 39 635, 38 930, and 40 322 cm–1, respectively, and the ionization threshold of In-As(CH3)3 is ~39 550 cm–1. The metal–ligand stretching frequencies are 143, 116, and 125 cm–1 for Ga+-P, In+-P, and Ga+-As, respectively, and 96 cm–1 for In-P. The intermolecular bending frequencies are 71, 65, and 42 cm–1 for Ga+-P-C, In+-P-C, and Ga+-As-C, respectively, and 47 cm–1 for In-P-C. In addition, ligand-based vibrational frequencies are determined for the CH3 wag, PC3 and AsC3 umbrella, and P-C stretching vibrations. Key words: ZEKE photoelectron, photoionization, DFT, gallium–phosphine, gallium–arsine, indium–phosphine, indium–arsine.

Ionization and Dissociation Energies of Group 13 Metal Complexes with Group 15 Hydrides

In this work, 1:1 complexes of the group 13 metal atoms with the group 15 hydrides are prepared with laser-ablation molecular beam techniques and studied with threshold photoionization and zero electron kinetic energy photoelectron spectroscopies and ab initio calculations. Ionization energies of the M−EH3 (M = Al, Ga, In; E = N, P, As) complexes increase in the order N < P ≤ As, whereas bond dissociation energies decrease down the group 15 hydrides. For a given hydride, the ionization and dissociation energies are different among the three metals, though the variation is smaller than that of the ligand effect. Ionization enhances the binding between the metal and ligand, and the enhancement is as large as three to five times.

Zero electron kinetic energy photoelectron spectroscopy of weakly bound In–NH2CH3, In–NH(CH3)2, and In–N(CH3)3 complexes

Single-photon pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy has been used to study the indium–methylamine complexes. The photoelectron spectra have been assigned using density functional theory and Franck–Condon calculations. The spectral assignments identify the symmetric In+–N stretch mode for In+–NH2CH3 (259 cm−1), In+–NH(CH3)2 (200 cm−1), and In+–N(CH3)3 (158 cm−1); In–N stretch for In–N(CH3)3 (110 cm−1); In+–N–C bend for In+–NH2CH3 (110 cm−1) and In+–NH(CH3)2 (120 cm−1); In–N–C bend for In–NH2CH3 (91 cm−1) and In–NH(CH3)2 (106 cm−1); and In+–N–H bend for In+–NH(CH3)2 (324 cm−1). Methyl substitutions for hydrogen atoms greatly influence the indium–nitrogen stretch forces and ionization potentials of the complexes. The indium–amine binding in these complexes includes orbital interaction and electrostatic forces.

Conformational studies of the neutral and cation of several substituted fluorenes

Abstract The S 1 excited state and cation ground state of various fluorene derivatives have been studied experimentally using resonance enhanced multiphoton ionization and zero electron kinetic energy photoelectron spectroscopy. The compounds studied are 2-propylfluorene, 9-fluoreneacetic acid and 2-propionylfluorene. Density functional quantum chemical calculations using the gaussian 98 program have been used to calculate the ground state and cation energies of each conformer as well as the barrier to interconversion via a bond rotation. These calculations, coupled with the experimental results, have led to the identification and assignment of the various conformations of these molecules.

Conformational energy and dynamics of 9-ethylfluorene

The S1 excited state and cation ground state of jet cooled 9-ethylfluorene have been studied experimentally using resonant enhanced multiphoton ionization and zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The spectroscopy has identified two conformations of the ethyl chain which are labeled symmetric and unsymmetric both of which exist in the supersonic expansion. Density functional quantum chemical calculations are used to calculate the ground state and cation energies of each conformer as well as the barrier to conformer interconversion via a bond rotation. Dynamics on the S1 surface are measured using picosecond and nanosecond ZEKE photoelectron spectroscopy. Fast irreversible vibrational redistribution is measured at energies ⩾990 cm−1 and the ZEKE spectra are shown to have a unique signature for each of the two isomers. Picosecond and nanosecond ZEKE spectroscopy are used to search for conformer interconversion but even at the highest energy probed (2648 cm−1) no evidence is seen for a dynamic barrier crossing. Statistical density of states calculations are used to predict the relative populations of each conformer expected as a function of excess energy as well as related Rice–Ramsperger–Kassel–Marcus calculations to predict the expected isomerization rates.

The structure of triniobium dinitride from zero electron kinetic energy photoelectron spectroscopy and density functional calculations

Zero electron kinetic energy photoelectron spectra are reported for Nb 3N 2. The geometry of the cluster was determined by comparing the experiments with density functional and Franck-Condon factor calculations. Both the neutral and cation have a three dimensional C 2v symmetry with each of the two nitrogen bridging two niobium atoms of the metal isosceles triangle. The symmetric deformation of niobium vibrations in the ion has a frequency of 257 cm −1. The asymmetric niobium stretching of the ion is 17 cm −1 larger than that of the neutral. Bonding between niobium and nitrogen is stronger in the ion than in the neutral.

Bend-stretch Fermi resonance in NO 2+ observed by delayed pulsed-field ionization zero-electron kinetic energy photoelectron spectroscopy

By means of zero-electron kinetic energy (ZEKE) threshold photoelectron spectroscopy, we examine bend-stretch Fermi resonance in NO 2 +. Accurate fundamental frequencies are obtained by using the (000) 3pσ Rydberg state as a reference state for all ionic vibrational ZEKE spectra. The degree of (100)–(02°0) Fermi resonance observed in NO 2 + is comparable to that found in the NO 2 3pσ Rydberg state, and results for both systems agree well with recent CCSD(T) and MRD-CI ab initio calculations. Comparison of the vibrational frequencies of the 3pσ Rydberg state and the cation suggests that the presence of the Rydberg electron slightly perturbs the harmonic potential and its second-order anharmonicities, but has little effect on the cubic coupling term associated with core Fermi resonance.