High resolution studies of low-energy electron attachment to SF5Cl: Product anions and absolute cross sections

Low energy electron attachment to SF$_5$Cl was studied at high energy resolution by mass spectrometric detection of the product anions. Two variants of the laser photoelectron attachment (LPA) technique (Kaiserslautern) were used for determining the threshold behaviour of the yield for SF$_5^-$ formation at about 1 meV resolution, and to investigate the relative cross sections for Cl$^-$, FCl$^-$, and SF$_5^-$ formation towards higher energies (up to 1 eV) at about 20 meV resolution. Thermal swarm measurements (Birmingham) were used to place the relative LPA cross sections on an absolute scale. A trochoidal electron monochromator (Innsbruck) was used for survey measurements of the relative cross sections for the different product anions over the energy range of 0-14 eV with a resolution of 0.30 eV. Combined with earlier beam data (taken at Berlin, J. Chem. Phys. 88 (1988) 149), the present experimental results provide a detailed set of partial cross sections for anion formation in low-energy electron collisions with SF$_5$Cl

Volatile Biomarkers in Breath Associated With Liver Cirrhosis — Comparisons of Pre- and Post-liver Transplant Breath Samples

AbstractBackgroundThe burden of liver disease in the UK has risen dramatically and there is a need for improved diagnostics.AimsTo determine which breath volatiles are associated with the cirrhotic liver and hence diagnostically useful.MethodsA two-stage biomarker discovery procedure was used. Alveolar breath samples of 31 patients with cirrhosis and 30 healthy controls were mass spectrometrically analysed and compared (stage 1). 12 of these patients had their breath analysed after liver transplant (stage 2). Five patients were followed longitudinally as in-patients in the post-transplant period.ResultsSeven volatiles were elevated in the breath of patients versus controls. Of these, five showed statistically significant decrease post-transplant: limonene, methanol, 2-pentanone, 2-butanone and carbon disulfide. On an individual basis limonene has the best diagnostic capability (the area under a receiver operating characteristic curve (AUROC) is 0.91), but this is improved by combining methanol, 2-pentanone and limonene (AUROC curve 0.95). Following transplant, limonene shows wash-out characteristics.ConclusionsLimonene, methanol and 2-pentanone are breath markers for a cirrhotic liver. This study raises the potential to investigate these volatiles as markers for early-stage liver disease. By monitoring the wash-out of limonene following transplant, graft liver function can be non-invasively assessed

Fragmentation of the valence electronic states of SeF6+ and TeF6+ studied by threshold photoelectron ? photoion coincidence spectroscopy

Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been performed on SeF$_6$ and TeF$_6$ and breakdown diagrams constructed. The ground electronic states of XF$_6^+$ (X = Se, Te) are repulsive in the Franck-Condon region, meaning that the first ion signal only gives an upper limit to the energy of the first dissociative ionisation pathway (XF$_5^+$ + F + e$^-$). Using TPEPICO time-of-flight spectra to determine the kinetic energy (KE) released in fragmentation over a range of energies, however, we have extrapolated to zero KE to calculate values of 14.1 $\pm$ 0.5 and 14.5 $\pm$ 0.6 eV for the first dissociative ionisation energy for SeF6 and TeF6, respectively. Upper limits for the enthalpies of formation of SeF$_4^+$, SeF$_3^+$, TeF$_4^+$ and TeF$_3^+$ at 0K are determined to be 426 $\pm$ 36, 368 $\pm$ 28, 428 $\pm$ 36 and 380 $\pm$ 28 kJ mol$^{-1}$, respectively

Vacuum-UV and electron dissociative ionisation studies of SF5Cl.

A complementary study of the interaction of SF$_5$Cl in the gas phase with vacuum-UV photons and low-energy electrons from the onset of ionisation, ca. 12 eV, to 20 eV is presented. The photon-induced experiments have used tunable vacuum-UV radiation from a synchrotron and threshold photoelectron photoion coincidence spectroscopy for product ion detection, the electron-induced experiments a trochoidal electron monochromator and a quadrupole mass spectrometer. The strengths and limitations of both experiments are contrasted, the main difference being the absence of state selectivity in the electron-induced study. The parent cation is not observed in either study, suggesting that its ground electronic state is repulsive following Franck-Condon vertical excitation. The fragment cations SF$_5^+$, SF$_4$Cl$^+$, SF$_4^+$ and SF$_3^+$ have been observed in both studies, with reasonable agreement in their threshold appearance energies. Using a variant of threshold photoelectron photoion coincidence spectroscopy applicable when the ground state of the parent cation is repulsive, the first dissociative ionisation energy of SF$_5$Cl is determined to be 12.3 ± 0.2 eV, leading to a value for the adiabatic ionisation energy for the SF$_5$ radical of 9.92 ± 0.28 eV. The electron-induced experiment is sensitive to ion-pair production, and onsets for F$^+$ and Cl$^+$ production have been observed which are only possible energetically if the accompanying fragments are the anions SF$_4$Cl$^-$ and SF$_5^-$, respectively. A lower limit for the electron affinity of the SF$_4$Cl radical of 4.88 eV is determined, a value confirmed by ab initio calculations. The electron-induced experiment is very sensitive to gas impurities, and the effects of minute quantities of SF$_4$, FCl, Cl$_2$ and possibly SF$_2$ in the gas sample are observed