RESUMO
Fluorinated species have a pivotal role in semiconductor material chemistry and some of them have been detected beyond the Earth's atmosphere. Achieving good energy accuracy on fluorinated species using quantum chemical calculations has long been a challenge. In addition, obtaining direct experimental thermochemical quantities has also proved difficult. Here, we report the threshold photoelectron and photoion yield spectra of SiF and CF radicals generated with a fluorine reactor. The spectra were analysed with the support of ab initio calculations, resulting in new experimental values for the adiabatic ionisation energies of both CF (9.128 ± 0.006 eV) and SiF (7.379 ± 0.009 eV). Using these values, the underlying thermochemical network of Active Thermochemical Tables was updated, providing further refined enthalpies of formation and dissociation energies of CF, SiF, and their cationic counterparts.
RESUMO
The first measurement of the photoelectron spectrum of the silylidyne free radical, SiH, is reported between 7 and 10.5 eV. Two main photoionizing transitions involving the neutral ground state, X+1Σ+ â X2Π and a+3Π â X2Π, are assigned by using ab initio calculations. The corresponding adiabatic ionization energies are derived, IEad(X+1Σ+) = 7.934(5) eV and IEad(a+3Π) = 10.205(5) eV, in good agreement with our calculated values and the previous determination by Berkowitz et al. [J. Chem. Phys. 86, 1235 (1987)] from a photoionization mass spectrometric study. The photoion yield of SiH recorded in this work exhibits a dense autoionization landscape similar to that observed in the case of the CH free radical [Gans et al., J. Chem. Phys. 144, 204307 (2016)].
RESUMO
A new experimental method has been developed to record photoelectron spectra based on the well-established pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy technique and inspired by the data treatment employed in slow photoelectron spectroscopy. This method has been successfully applied to two well-known systems: the X+2Πg,1/2(v+ = 0) â X1Σ+g(v = 0) and the X+1Σ+(v+ = 2) â X2Π1/2(v = 0) ionizing transitions of CO2 and NO, respectively. The first results highlight several advantages of our technique such as an improved signal-to-noise ratio without degrading the spectral resolution and a direct field-free energy determination. The data obtained for NO indicate that this method might be useful for studying field-induced autoionization processes.
