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Electronic spectroscopy of AuCH2+ and intermediates involved in the conversion of methane to methanol by FeO+

Fernando Aguirre, University of Massachusetts - Amherst

Abstract

The conversion of a cheap and plentiful starting material such as natural gas into valuable products or starting materials for another industrial process (e.g. polymerization) is one of today's most tantalizing catalytic challenges. In the gas phase, FeO+ has met this challenge by directly converting methane to methanol at thermal conditions. A description of significant advances obtained in the understanding of this reaction, e.g. reaction rates and mechanism, as well as the driving force for the spectroscopic study of its reaction intermediates is presented in Chapter I. The experimental apparatus and a general description of the data generated in this study are presented in Chapter II. ^ The complete photodissociation study of AuCH2+ is presented in Chapter III. The experimental study of third-row transition-metal MCH2+ complexes is of great interest, considering that if Do0(M+ − CH2) ≥ 464 kJ mol−1 indicates that activation of methane is exothermic and occurs readily with the corresponding metal cation, as in the case for M = Ta+, W+, Ir+, Os + and Pt+. In this chapter we describe the influence of relativistic effects in the photodissociation of AuCH2 + as well as the effect of parent rotational energy on the photodissociation threshold. The experimental study of this closed-shell molecule serves to assess the general reliability of theoretical methods applied to third-row transition metal compounds. ^ In Chapter IV the photodissociation spectra of intermediates of the FeO + + CH4 reaction, specifically [H2C = Fe–OH 2]+ and [HO–Fe–CH3]+ are discussed. The spectra present vibrationally resolved peaks, assigned to the Fe–C stretch mode in both intermediates. Additional features observed in the spectrum of [HO–Fe–CH3]+ are assigned to the Fe–O stretch and the O–Fe–C bend. The analysis of the spectra is aided by theoretical calculations at the Hartree-Fock/density-functional (B3LYP) level performed on both intermediates and time-dependent density functional theory (TD-DFT) calculations performed on FeCH2+ to predict excited electronic states. ^ In photodissociation the spectral resolution is often limited by the lifetime of the excited state reached after photon absorption. On way to overcome this limitation is by resonant two-photon dissociation, which probes an intermediate state below the dissociation threshold. In Chapter V the rotationally resolved spectrum of the (8,0) and (9,0) bands of the 6Π ← 6Σ+ system of FeO+ is studied. This is the first observation of the 6Π state of FeO + and analysis of this system gives the first set of rotational constants of the 6Σ+ ground state of FeO +. The assignment of the electronic transition observed is supported by TD-DFT calculations performed on FeO+. ^

Subject Area

Chemistry, Physical

Recommended Citation

Fernando Aguirre, "Electronic spectroscopy of AuCH2+ and intermediates involved in the conversion of methane to methanol by FeO+" (January 1, 2002). Doctoral Dissertations Available from Proquest. Paper AAI3039333.
http://scholarworks.umass.edu/dissertations/AAI3039333

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