Determination Of Photoionization Cross Sections Research Articles

Measurements of mass attenuation coefficients and determination of photoionization cross sections at energies across the Li (i=1–3) edges of 66Dy

The absolute values of the mass attenuation coefficients have been measured at sixty two photon energies across the Li (i=1–3) sub-shell absorption edges of 66Dy covering the region 7.6–14.0keV in order to investigate the influence of near-edge processes on the attenuation coefficients. The present measured attenuation coefficients are found to be higher by up to 10% than the theoretical values evaluated from the computer code XCOM (Berger et al., 2010) and the self-consistent Dirac-Hartree-Slater (DHS) model based values tabulated by Chantler (1995) over the energy region 7.6–14.0keV, except at energies in vicinity (few eV) of the Li (i=1–3) sub-shell absorption edge energies where the measured values are significantly higher (up to 37%) than both the sets of theoretical values. Further, the Li (i=1–3) sub-shell photoionization cross sections, (σLiP)exp, deduced from the present measured mass attenuation coefficients are compared with the non-relativistic Hartree-Fock-Slater (HFS) model based values tabulated by Scofield (1973) and those evaluated from the theoretical total photoionization attenuation coefficients tabulated by Chantler (1995). The deduced (σLiP)exp(i=1–3) values are found to be in better agreement with those evaluated from the tabulations given by Chantler (1995) than the values given by Scofield (1973) over the energy region 7.8 – 14.0keV included in this study. However, at photon energies up to few eV above the Li edges, the deduced (σLiP)exp(i=1–3) values are found to be significantly higher (up to 32%) than both the sets of theoretical values.

Online Comprehensive Two-Dimensional Characterization of Puff-by-Puff Resolved Cigarette Smoke by Hyphenation of Fast Gas Chromatography to Single-Photon Ionization Time-of-Flight Mass Spectrometry: Quantification of Hazardous Volatile Organic Compounds

This work presents the direct coupling of a custom-made smoking machine (SM) to fast gas chromatography combined with single-photon ionization mass spectrometry (GC × SPI-MS) utilizing a six-port, two-position valve for online puff-resolved comprehensive two-dimensional investigation of cigarette smoke. The innovative electron-beam pumped rare gas excimer light source (EBEL) filled with argon provided vacuum ultraviolet (VUV) photons of 9.8 ± 0.4 eV (126 ± 9 nm) for SPI. Puff-by-puff quantification of 14 hazardous volatile organic smoke constituents from the 2R4F Kentucky research cigarette was enabled for two smoking regimes, i.e., ISO and Canadian Intense, after determination of photoionization cross sections. The investigated analytes comprised NO, acetaldehyde, butadiene, acrolein, propanal, acetone, isoprene, furan, crotonaldehyde, isobutanal, butanal, 2-butanone, benzene, and toluene. The determined amounts of these compounds in cigarette smoke agreed excellently with the literature values. Furthermore, the two well-known patterns of puff-by-puff behaviors for these different smoke constituents were obtained for both whole smoke and gas-phase measurements.

HeI α photoelectron modulation spectroscopy of H2 and D2

A new method for the determination of photoionization cross sections is presented. The technique is used to obtain cross sections of H2 and D2 relative to those of H and D atoms from accurate HeI α photoelectron intensity measurements. With the virtually exact atomic cross section calculations available for H and D atoms our experiments provide absolute H2 and D2 photoionization cross sections. Ultraviolet photoelectron (UV PE) spectra of vibrationally excited hydrogen (v″=1,2) and deuterium (v″=1,2,3), free from overlapping bands due to vibrational ground state molecules, are presented for the first time. Positions and intensities of all observed features are excellently reproduced using well-known molecular and ionic constants and accurate ab initio potential energy curves. Combination of the cross section determinations of H2 and D2 with intensity measurements of vibrationally excited H2 and D2 reveals some qualitative information on H*2 and D*2 cross sections and β parameters.