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

Abstract

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.

Binding sites, rotational conformers, and electronic states of Sc–C6H5X (X=F, CH3, OH, and CN) probed by pulsed-field-ionization electron spectroscopy

“…27 The field dependence of the ZEKE signal was not measured because the energy shift from the small electric field ͑1.2 V/cm͒ has been shown to be much smaller than the spectral linewidth. 28 Calculations of molecular geometries and vibrational frequencies were carried out with GAUSSIAN03 program package. 29 The B3LYP ͑Becke's three parameter hybrid functional with the correlation functional of Lee, Yang, and Parr͒ functional was selected because previous studies have shown that this method yielded good agreement with experimental ZEKE spectra of metal-aromatic complexes.…”

“…29 The B3LYP ͑Becke's three parameter hybrid functional with the correlation functional of Lee, Yang, and Parr͒ functional was selected because previous studies have shown that this method yielded good agreement with experimental ZEKE spectra of metal-aromatic complexes. 28,30,31 In these calculations, the all electron 6-311+ G͑d , p͒ basis was used for all atoms.…”

Two photon resonant excitation of Copper–Rydberg levels

“…High lying Rydberg states of atoms and molecules have found interest in general [1][2][3][4] and particular utility in various spectroscopies; pulsed field ionization-zero electron kinetic energy (PFI-ZEKE) [5][6][7][8] and threshold ionization mass spectrometry [9][10][11][12][13] to name a few. Both techniques rely on the ability to optically pump electronic transitions to Rydberg energy levels near ionization.…”

Probing the bonding and structures of metal-organic radicals with zero energy electrons

“…[8] and the ZEKE spectrum from ref. [13]. The spectral resolution of the ZEKE spectrum is about one-hundred times better than that of the He 1 spectrum.…”

“…In this figure, the He I photoelectron spectrum of bis(benzene)chromium is broad (~ 60 meV) [8], whereas its ZEKE spectrum is very sharp (~ 0.6 meV) with well-resolved metal-ligand vibrational structures [13]. ZEKE is different from traditional photoelectron spectroscopy in that ionization is not direct but stepwise (Figure 2).…”