Photodissociation Spectroscopy and Photofragment Imaging of the Fe⁺(Acetylene) Complex

Abstract

Tunable laser photodissociation spectroscopy in the 700−400 nm region and photofragment imaging experiments are employed to investigate the Fe + (acetylene) ion−molecule complex. At energies above a threshold at 679 nm, continuous dissociation is detected throughout the visible wavelength region, with regions of broad structure. Comparison to the spectrum predicted by time-dependent density functional theory (TD-DFT) indicates that the complex has a quartet ground state. The dissociation threshold for Fe + (acetylene) at 679 nm provides the dissociation energy on the quartet potential energy surface. Correction for the atomic quartet−sextet spin state energy difference provides an adiabatic dissociation energy of 36.8 ± 0.2 kcal/ mol. Photofragment imaging of the Fe + photoproduct produced at 603.5 nm produces significant kinetic energy release (KER). The photon energy and the maximum value of the KER provide an upper limit on the dissociation energy of D 0 ≤ 34.6 ± 3.2 kcal/mol. The dissociation energies determined from the spectroscopy and photofragment imaging experiments agree nicely with the value determined previously by collision-induced dissociation (38.0 ± 2.6 kcal/mol). However, both values are significantly lower than those produced by computational chemistry at the DFT level using different functionals recommended for transition-metal chemistry.

Photodissociation Spectroscopy and Photofragment Imaging to Probe Fe+(Benzene)1,2 Dissociation Energies

“…Because all three experiments agree with each other, it seems that this may be true. A similar situation was found recently for the Fe + (acetylene) complex, where CID, the scanned threshold, and photofragment imaging all produced the same dissociation energies . In the Fe + (acetylene) system, the dissociation energies determined (34–38 kcal/mol) were all lower than the values found here for the Fe + (benzene) complex.…”

“…A similar situation was found recently for the Fe + (acetylene) complex, where CID, the scanned threshold, and photofragment imaging all produced the same dissociation energies. 68 In the Fe + (acetylene) system, the dissociation energies determined (34−38 kcal/mol) were all lower than the values found here for the Fe + (benzene) complex. The computed values for the dissociation energies for Fe + (acetylene) were in poor agreement with DFT theory using B3LYP, M06-L, or MN15-L functionals.…”

“…If these conditions do not apply, the method provides an upper limit to the bond energy. This method of determining the dissociation energy has been applied previously to transition-metal complexes and to their metal dimers. − In a second method applicable only to Fe + (benzene), we employ photofragment imaging of the benzene cation produced at higher-energy excitation via a charge-transfer dissociation process. We have described this method previously in studies of silver ion complexes with benzene and other similar aromatic ligands. , These methods provide determinations of the dissociation energy for these complexes independent from previous CID measurements.…”

“…This method of determining the dissociation energy has been applied previously to transition-metal complexes and to their metal dimers. 62 − 68 In a second method applicable only to Fe + (benzene), we employ photofragment imaging of the benzene cation produced at higher-energy excitation via a charge-transfer dissociation process. We have described this method previously in studies of silver ion complexes with benzene and other similar aromatic ligands.…”

Charge-Transfer Spectroscopy of Ag+(Benzene) and Ag+(Toluene)

“…Cation−π interactions mediate enzyme–substrate binding, antigen–antibody recognition, and protein folding. Similar bonding influences organometallic catalysis, including the binding of “single site”-supported metal catalysts on the surfaces of graphite, graphene, or carbon nanotubes, and the interactions at metal centers in metal–organic frameworks (MOFs). − The same chemical forces active in these more complex chemical environments are also found in isolated organometallic complexes and their ions. − Organometallic ions have been studied in mass spectrometry for many years − and investigated extensively with theory. − More recent experiments have applied infrared and electronic spectroscopy to these systems. − In the present work, we investigate these interactions through electronic spectroscopy of mass-selected silver–benzene and silver–toluene cation complexes.…”