Ionization of Atoms by Slow Heavy Particles, Including Dark Matter

Atoms and molecules can become ionized during the scattering of a slow, heavy particle off a bound electron. Such an interaction involving leptophilic weakly interacting massive particles (WIMPs) is a promising possible explanation for the anomalous 9σ annual modulation in the DAMA dark matter direct detection experiment [R. Bernabei et al., Eur. Phys. J. C 73, 2648 (2013)]. We demonstrate the applicability of the Born approximation for such an interaction by showing its equivalence to the semiclassical adiabatic treatment of atomic ionization by slow-moving WIMPs. Conventional wisdom has it that the ionization probability for such a process should be exponentially small. We show, however, that due to nonanalytic, cusplike behavior of Coulomb functions close to the nucleus this suppression is removed, leading to an effective atomic structure enhancement. We also show that electron relativistic effects actually give the dominant contribution to such a process, enhancing the differential cross section by up to 1000 times.

Ionization in atmospheres of brown dwarfs and extrasolar planets. V. Alfvén Ionization

Observations of continuous radio and sporadic X-ray emission from low-mass objects suggest they harbor localized plasmas in their atmospheric environments. For low-mass objects, the degree of thermal ionization is insufficient to qualify the ionized component as a plasma, posing the question: what ionization processes can efficiently produce the required plasma that is the source of the radiation? We propose Alfv´en ionization as a mechanism for producing localized pockets of ionized gas in the atmosphere, having sufficient degrees of ionization ( 10−7) that they constitute plasmas. We outline the criteria required for Alfv´en ionization and demonstrate its applicability in the atmospheres of low-mass objects such as giant gas planets, brown dwarfs, and M dwarfs with both solar and sub-solar metallicities. We find that Alfv´en ionization is most efficient at mid to low atmospheric pressures where a seed plasma is easier to magnetize and the pressure gradients needed to drive the required neutral flows are the smallest. For the model atmospheres considered, our results show that degrees of ionization of 10−6–1 can be obtained as a result of Alfv´en ionization. Observable consequences include continuum bremsstrahlung emission, superimposed with spectral lines from the plasma ion species (e.g., He, Mg, H2, or CO lines). Forbidden lines are also expected from the metastable population. The presence of an atmospheric plasma opens the door to a multitude of plasma and chemical processes not yet considered in current atmospheric models. The occurrence of Alfv´en ionization may also be applicable to other astrophysical environments such as protoplanetary disks.

Electric field strengths and ion trajectories in sharp-edge field ionization sources

On the presumption that a sharp edge may be represented by a hyperbola, a conformal transformation method is used to derive electric field equations for a sharp edge suspended above a flat plate. A further transformation is then introduced to give electric field components for a sharp edge suspended above a thin slit. Expressions are deduced for the field strength at the vertex of the edge in both arrangements. The calculated electric field components are used to compute ion trajectories in the simple edge/flat-plate case. The results are considered in relation to future study of ion focusing and unimolecular decomposition of ions in field ionization mass spectrometers.

Calculated ionization potentials of the linear alkanes

The equivalent orbital (EO) method is investigated and used for predicting outer and inner ionization potentials of the linear alkanes. The calculated ionization potentials are in good agreement with those observed in photoelectron spectra provided that a set of 12 parameters is used in the theory. An optimization technique is used to find the best values for thle parameters and a single transferable parameter set can be found which is applicable to all the n-alkanes. A good fit to the experimental results can only be obtained if the uppermost molecular orbital of the n-alkanes is an antisymmetrical orbital built up from CH equivalent orbitals.

Identification and characterization of shallow impurity states in gallium arsenide and indium phosphide using photothermal ionization spectroscopy

A model of far infrared (FIR) dielectric response of shallow impurity states in a semiconductor has been developed and is presented for the specific case of the shallow donor transitions in high purity epitaxial GaAs. The model is quite general, however, and should be applicable with slight modification, not only to shallow donors in other materials such as InP, but also to shallow acceptors and excitons. The effects of the enormous dielectric response of shallow donors on the FIR optical properties of reflectance, transmittance, and absorptance, and photoconductive response of high purity epitaxial GaAs films are predicted and compared with experimental photothermal ionization spectra. The model accounts for many of the peculiar features that are frequently observed in these spectra, one of which was the cause of erroneous donor identifications in the early doping experiments. The model also corrects some commonly held misconceptions concerning photo-thermal ionization peak widths and amplitudes and their relationships to donor and acceptor concentrations. These corrections are of particular relevance to the proper interpretation of photothermal ionization spectra in the study of impurity incorporation in high purity epitaxial material. The model also suggests that the technique of FIR reflectance, although it has not been widely employed, should be useful in the study of shallow impurities in semiconductors.

The experimental determination of impact ionization coefficients in gallium arsenide and indium phosphide

U of I Only

Investigating the cosmic-ray ionization rate in the galactic interstellar medium through observations of H3+

Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H3+ observations to 50, with detections in 21 of those. Ionization rates inferred from these detections are in the range (1.7+-1.0)x10^-16 s^-1 < zeta_2 < (10.6+-6.8)x10^-16 s^-1 with a mean value of zeta_2=(3.3+-0.4)x10^-16 s^-1. Upper limits (3sigma) derived from non-detections of H3+ are as low as zeta_2 < 0.4x10^-16 s^-1. These low upper-limits, in combination with the wide range of inferred cosmic-ray ionization rates, indicate variations in zeta_2 between different diffuse cloud sight lines. Calculations of the cosmic-ray ionization rate from theoretical cosmic-ray spectra require a large flux of low-energy (MeV) particles to reproduce values inferred from observations. Given the relatively short range of low-energy cosmic rays --- those most efficient at ionization --- the proximity of a cloud to a site of particle acceleration may set its ionization rate. Variations in zeta_2 are thus likely due to variations in the cosmic-ray spectrum at low energies resulting from the effects of particle propagation. To test this theory, H3+ was observed in sight lines passing through diffuse molecular clouds known to be interacting with the supernova remnant IC 443, a probable site of particle acceleration. Where H3+ is detected, ionization rates of zeta_2=(20+-10)x10^-16 s^-1 are inferred, higher than for any other diffuse cloud. These results support both the concept that supernova remnants act as particle accelerators, and the hypothesis that propagation effects are responsible for causing spatial variations in the cosmic-ray spectrum and ionization rate. Future observations of H3+ near other supernova remnants and in sight lines where complementary ionization tracers (OH+, H2O+, H3O+) have been observed will further our understanding of the subject.

High-performance liquid chromatography (HPLC) and high-performance liquid chromatography mass spectrometry (HPLC/MS) for the analysis of date rape drugs

The drugs studied in this work have been reportedly used to commit drug-facilitated sexual assault (DFSA), commonly known as "date rape". Detection of the drugs was performed using high-performance liquid chromatography with ultraviolet detection (HPLC/UV) and identified with high performance-liquid chromatography mass spectrometry (HPLC/MS) using selected ion monitoring (SIM). The objective of this study was to develop a single HPLC method for the simultaneous detection, identification and quantitation of these drugs. The following drugs were simultaneously analyzed: Gamma-hydroxybutyrate (GHB), scopolamine, lysergic acid diethylamide, ketamine, flunitrazepam, and diphenhydramine. The results showed increased sensitivity with electrospray (ES) ionization versus atmospheric pressure chemical ionization (APCI) using HPLC/MS. HPLC/ES/MS was approximately six times more sensitive than HPLC/APCI/MS and about fifty times more sensitive than HPLC/UV. A limit of detection (LOD) of 100 ppb was achieved for drug analysis using this method. The average linear regression coefficient of correlation squared (r2) was 0.933 for HPLC/UV and 0.998 for HPLC/ES/MS. The detection limits achieved by this method allowed for the detection of drug dosages used in beverage tampering. This method can be used to screen beverages suspected of drug tampering. The results of this study demonstrated that solid phase microextraction (SPME) did not improve sensitivity as an extraction technique when compared to direct injections of the drug standards.

High-throughput Analysis By Sp-ldi-ms For Fast Identification Of Adulterations In Commercial Balsamic Vinegars.

Balsamic vinegar (BV) is a typical and valuable Italian product, worldwide appreciated thanks to its characteristic flavors and potential health benefits. Several studies have been conducted to assess physicochemical and microbial compositions of BV, as well as its beneficial properties. Due to highly-disseminated claims of antioxidant, antihypertensive and antiglycemic properties, BV is a known target for frauds and adulterations. For that matter, product authentication, certifying its origin (region or country) and thus the processing conditions, is becoming a growing concern. Striving for fraud reduction as well as quality and safety assurance, reliable analytical strategies to rapidly evaluate BV quality are very interesting, also from an economical point of view. This work employs silica plate laser desorption/ionization mass spectrometry (SP-LDI-MS) for fast chemical profiling of commercial BV samples with protected geographical indication (PGI) and identification of its adulterated samples with low-priced vinegars, namely apple, alcohol and red/white wines.