Fernando Aguirre

Vibrationally resolved photofragment spectroscopy of FeO

We report the first vibrationally resolved spectroscopic study of FeO+. We observe the 0←0 and 1←0 bands of a 6Σ←X 6Σ transition at 28 648.7 and 29 311 cm−1. Under slightly modified source conditions the 1←1 transition is observed at 28 473 cm−1. In addition to establishing an upper limit D0o(Fe+–O)⩽342.7 kJ/mol, our results give the first experimental measurements of the vibrational frequencies in both the ground state, ν0″=838±4 cm−1, and the excited electronic state, ν0′=662±2 cm−1. Partially resolved rotational structure underlying the vibrational peaks has been analyzed to measure the predissociation lifetime and estimate the change in molecular constants upon electronic excitation.

Electronic spectroscopy of intermediates involved in the conversion of methane to methanol by FeO

Specific ion–molecule reactions are used to prepare two intermediates of the FeO++CH4 reaction, and photodissociation of the jet-cooled intermediates is examined in the visible and near-ultraviolet using time-of-flight mass spectrometry. The photodissociation spectrum of the aquo iron carbene complex [H2C=Fe–OH2]+ shows transitions to at least four excited electronic states in the FeCH2+ chromophore, with broad vibrational structure. Photoexcitation of the insertion intermediate [HO–Fe–CH3]+ leads to formation of FeOH++CH3 and also triggers the reaction to produce Fe++CH3OH. The photodissociation spectrum of [HO–Fe–CH3]+ presents a vibrationally resolved band involving progressions in the excited state Fe–C stretch, Fe–O stretch, and O–Fe–C bend. The change in the Fe–C bond length in [HO–Fe–CH3]+ and [H2C=Fe–OH2]+ upon photoexcitation is calculated from a Franck–Condon analysis of the vibronic features observed. The analysis of the experimental results is aided by hybrid Hartree–Fock/density-functional (B...

Gas-phase photodissociation of AuCH2 +: The dissociation threshold of jet-cooled and rotationally thermalized ions

Abstract The photofragment spectra of jet-cooled and rotationally thermalized AuCH2+ are reported. Two channels are observed: loss of H2 and loss of CH2 with a branching ratio of 1.4:1 over the region studied. The presence of a threshold at 322 nm for the dissociation of jet-cooled AuCH2+ to Au++CH2 implies the upper limitD0o(Au+–CH2)≤372±3 kJ mol−1. The dissociation threshold of ions rotationally thermalized in an ion trap shifts to lower energy by the amount of parent rotational energy.

The low-lying electronic states of FeO+: Rotational analysis of the resonance enhanced photodissociation spectra of the 6Π7/2←X 6Σ+ system

The resonance enhanced (1+1) photodissociation spectra of the (8,0) and (9,0) bands of the 6Π7/2←6Σ+ system of FeO+ have been recorded. From a rotational analysis, the rotational parameters for the 6Σ+ ground state of FeO+ have been obtained for the first time. The rotational constant B0=0.5020±0.0004 cm−1 is derived, giving r0=1.643±0.001 A. Other molecular parameters determined for the 6Σ+ ground state are the spin–spin coupling constant, λ=−0.126±0.006 cm−1, and the spin–rotational coupling constant, γ=−0.033±0.002 cm−1. The assignment of the upper state as 6Π7/2 is based on the characteristic appearance of the band and on time-dependent density functional (TD-DFT) calculations performed on FeO+. The reliability of the TD-DFT method in the prediction of excited states of FeO+ is corroborated by calculations on CrF and MnO, which have been extensively characterized either by spectroscopy or by high-level theoretical calculations.

Photodissociation spectra of transition metal sulfides: spin–orbit structure in charge transfer bands of FeS+ and NiS+

Abstract Photofragment spectra of FeS+ and NiS+ are reported. Analysis of the FeS+ spectrum reveals it to arise from a 6 Π← 6 Σ charge-transfer transition, and gives the vibrational frequency, ω e ′ =295 cm −1 , and spin–orbit constant, |A|=125 cm −1 , in the 6 Π state. The onset of the NiS+ spectrum appears to occur in the middle of a vibrational progression, thus giving a precise measurement of the Ni+–S bond strength, D 0 ( Ni + –S )=238±4 kJ mol −1 . Analysis of the spectrum for vibrational and spin–orbit structure leads to a tentative assignment of a 4 Δ ground state and suggests the spectrum is composed of overlapping transitions to two near-degenerate excited electronic states, most likely a 4 Π and 4 Φ pair.