Bradford R. Sohnlein

Pulsed-field ionization electron spectroscopy of group 6 metal (Cr, Mo, and W) bis(benzene) sandwich complexes.

Group 6 metal bis(benzene) sandwich complexes (M-bz(2): M=Cr, Mo, and W and bz=C(6)H(6)) were produced with laser vaporization molecular beam techniques and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and density functional theory calculations. Each sandwich complex is in a D(6h) eclipsed configuration with (1)A(1g) and (2)A(1g) as the neutral and cationic ground electronic states, respectively. The adiabatic ionization energies for Cr-, Mo-, and W-bz(2) are measured to be 44,081(7), 44,581(10), and 43,634(7) cm(-1), respectively. The metal-benzene stretch and benzene torsion frequencies of the ion are measured to be 264, 277, and 370 cm(-1) and 11, 21, and 45 cm(-1) for Cr-, Mo-, and W-bz(2), respectively. In addition, a C-H out-of-plane bending mode is measured to be 787 cm(-1) for the Cr(+)-bz(2) complex, while a C-C in-plane bending mode is measured to be 614 cm(-1) for the W(+)-bz(2) complex. The unusual trend in the ionization energy and metal-benzene stretch frequency indicates strong relativistic effects on tungsten binding.

Pulsed-field ionization electron spectroscopy and binding energies of alkali metal-dimethyl ether and -dimethoxyethane complexes

Lithium and sodium complexes of dimethyl ether (DME) and dimethoxyethane (DXE) were produced by reactions of laser-vaporized metal atoms with organic vapors in a pulsed nozzle cluster source. The mono-ligand complexes were studied by photoionization and pulsed field ionization zero electron kinetic energy (ZEKE) spectroscopy. Vibrationally resolved ZEKE spectra were obtained for Li(DME), Na(DME) and Li(DXE) and a photoionization efficiency spectrum for Na(DXE). The ZEKE spectra were analyzed by comparing with the spectra of other metal-ether complexes and with electronic structure calculations and spectral simulations. Major vibrations measured for the M(DME) (M=Li,Na) ions were M-O and C-O stretches and M-O-C and C-O-C bends. These vibrations and additional O-Li-O and O-C-C-O bends were observed for the Li(DXE) ion. The M(DME) complexes were in C2v symmetry with the metal atom binding to oxygen, whereas Li(DXE) was in a C2 ring configuration with the Li atom attaching to both oxygen atoms. Moreover, the ionization energies of these complexes were measured from the ZEKE or photoionization spectra and bond dissociation energies were derived from a thermodynamic cycle.

Electron-spin multiplicities and molecular structures of neutral and ionic scandium-benzene complexes

Scandium-benzene complexes, Sc-(C6H6)1,2 are produced by interactions between the laser-vaporized scandium atoms and benzene vapor in pulsed molecular beams, and identified by photoionization time-of-flight mass spectrometry and photoionization efficiency spectroscopy. The electron-spin multiplicities and geometries of these complexes and their ions are determined by combining pulsed field-ionization zero electron kinetic-energy spectroscopy and density-functional theory calculations. For scandium-monobenzene, a short-range quartet ground state is determined for the neutral complex, and a low-energy triplet state is probed for the ion. For the dibenzene complex, the neutral ground state is a doublet, and two low-energy ion states are singlet and triplet. The quartet and triplet states of scandium-monobenzene and the triplet state of scandium-dibenzene possess sixfold symmetry, whereas the doublet and singlet of the dibenzene complex have twofold symmetry. Moreover, ionization energies and metal-ring stretching wavenumbers are measured for both complexes.

Electronic states of neutral and cationic bis(benzene) titanium and vanadium sandwich complexes studied by pulsed field ionization electron spectroscopy

Ti- and V-bz2 (bz=C6H6) sandwich complexes have been prepared in a laser-ablation cluster beam source and studied by pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy and theoretical calculations. The ground electronic states of the neutral Ti- and V-bz2 complexes are determined to be 1A1g and 2A1g, and their ionization energies are measured to be 5.732+/-0.001 and 5.784+/-0.002 eV, respectively. These neutral complexes have eta6 binding and are in an eclipsed D6h configuration with flat benzene rings. Ionization of the 1A1g and 2A1g neutral states of Ti- and V-bz2 yields the 2B1g and 3B1g ion states, respectively, in a D2h point group with slightly puckered benzene rings. In addition, the binding and structures of these two complexes are compared with other first-row transition metal bis(benzene) sandwiches.

A photoionization and photoelectron study of vibrational and electronic cooling in metal molecular beams

Abstract Threshold photoionization and pulsed-field-ionization zero-electron-kinetic-energy photoelectron spectra have been used to study the vibrational cooling of Cu–N(CH 3 ) 3 and the electronic cooling of Al–NH 3 in helium and argon supersonic jets. The vibrational temperatures of Cu–N(CH 3 ) 3 are estimated to be ∼40 K in argon and ∼120 K in helium, whereas the electronic temperatures of Al–NH 3 are about 20 and 80 K, respectively. Argon more efficiently cools the internal degrees of freedom of the metal systems, but helium provides additional spectroscopic information about the neutral molecules. The differences in the observed spectra have greatly facilitated spectral assignments for these complexes.

Spectroscopy and calculations of weakly bound gallium complexes with ammonia and monomethylamine

The gallium complexes were produced in pulsed molecular beams and studied with zero electron kinetic energy (ZEKE) photoelectron spectroscopy. Intermolecular vibrational frequencies and adiabatic ionization potentials (IPs) were obtained from ZEKE spectra. Ground electronic states were identified by combining the ZEKE spectra with quantum chemical and Franck–Condon calculations. Ga–NH3 has an IP of 40 135 cm−1 and metal-ligand stretching frequencies of 270 cm−1 (ωs+) in the ion and 161 cm−1 (νs) in the neutral. The IP of Ga–NH2CH3 is 39 330 cm−1, and the vibrational frequencies are 93 cm−1 (νb) for the Ga–N–C bending, 124 cm−1 (ωb+) for the Ga+–N–C bending, and 299 cm−1 (ωs+) for the Ga+–N stretching. The strength of the gallium–methylamine binding is stronger than that of the gallium–ammonia. The ground state of Ga–NH3 is 2A′(Cs) and that of Ga+–NH3 is 1A1(C3v). In contrast, Ga–NH2CH3 has two doublets, 2A′ and 2A″(Cs), with virtually the same energies, whereas Ga+–NH2CH3 has a 1A′(Cs) ground state.

Pulsed-field ionization zero electron kinetic energy spectroscopy and theoretical calculations of copper complexes: Cu–X(CH3)3 (X=N,P,As)

The copper complexes were produced in pulsed laser vaporization molecular beams and investigated by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and second-order Moller–Plesset (MP2) perturbation and hybrid B3LYP density functional theory calculations. The ground electronic states of Cu–X(CH3)3 and Cu+–X(CH3)3 (X=N,P,As) are 2A1 and 1A1, respectively, both with C3v symmetry. From the ZEKE spectra, the adiabatic ionization potentials of the neutral molecules are determined to be 44 730, 41 508, and 42 324 cm−1, and the Cu+/Cu–X stretching frequencies are 268/199, 214/187, and 188/155 cm−1 for X=N, P, and As, respectively. The degenerate Cu+/Cu–P–C and Cu+/Cu–As–C bending frequencies are measured to be 146/83 and 118/52 cm−1, while the Cu+/Cu–N–C mode was not observed. In addition, the CH3 wag, X–C stretching, and XC3 umbrella modes are also measured for the phosphine and arsine complexes. From the MP2 theory, the dissociation energies of the Cu+ and Cu complexes are estimated to...

Zero electron kinetic energy photoelectron spectroscopy and density functional theory calculations of gallium-methylamine complexes

Gallium–dimethylamine and –trimethylamine were produced in pulsed laser vaporization molecular beams and studied by threshold photoionization and pulsed-field ionization zero electron kinetic energy (ZEKE) photoelectron spectroscopies and density functional theory calculations. Analyses of the ZEKE spectra yield molecular adiabatic ionization potentials and metal–ligand and ligand-based vibrational frequencies. Comparisons of the experimental and theoretical results establish the ground electronic states of the neutral and ionic complexes. The ionization potentials, Ga+/Ga–N stretching, and Ga+/Ga–N–C bending frequencies are 38 790, 206/177, and 132/128 cm−1 for the dimethylamine complex and 38 081 cm−1, 188/133, and 111/92 cm−1 for the trimethylamine species. The electronic ground states are 1A′/2A′ for Ga+/Ga–NH(CH3)2 and 1A1/2A″ for Ga+/Ga–N(CH3)3. The calculated metal–ligand binding energies of Ga+/Ga–NH(CH2)2 and –N(CH3)3 are 36.2/9.7 and 37.1/8.5 kcal mol−1, respectively.

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.

Photoelectron spectroscopy and density functional theory of puckered ring structures of Group 13 metal-ethylenediamine.

The ethylenediamine (en) complexes of Al, Ga, and In atoms were prepared in laser-vaporization supersonic molecular beams and studied with pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and density functional theory. Several conformers of each metal complex are obtained by B3LYP calculations, and a five-membered cyclic structure is identified by combining the experimental measurements and theoretical calculations. Adiabatic ionization potentials, vibrational frequencies, and bond dissociation energies are determined for the ring structure. The ionization potentials of the Al, Ga, and In species are measured to be 32 784 (5), 33 324 (5), and 33 637 (7) cm(-1), respectively, and metal-ligand dissociation energies of the ionic and neutral complexes are calculated to be 60.2/16.2 (Al(+)/Al), 55.5/13.0 (Ga(+)/Ga), and 50.0/11.4 (In(+)/In) kcal mol(-1). Metal-ligand stretch and bend as well as a number of ligand-based vibrations are measured. Harmonic frequencies and anharmonicities of the M(+)-N (M=Al,Ga,In) stretch are determined for all three M(+)-en ions and the C-C-N bend of Ga(+)-en and In(+)-en. In comparison to monodentate methylamine, the bidentate binding of ethylenediamine leads to a significantly lower ionization potential and higher metal-ligand bond strength of the metal complexes.