Showing papers by "Sydney Leach published in 2012"

Survival of plant seeds, their UV screens, and nptII DNA for 18 months outside the International Space Station.

Abstract: The plausibility that life was imported to Earth from elsewhere can be tested by subjecting life-forms to space travel. Ultraviolet light is the major liability in short-term exposures (Horneck et al., 2001), and plant seeds, tardigrades, and lichens—but not microorganisms and their spores—are candidates for long-term survival (Anikeeva et al., 1990; Sancho et al., 2007; Jonsson et al., 2008; de la Torre et al., 2010). In the present study, plant seeds germinated after 1.5 years of exposure to solar UV, solar and galactic cosmic radiation, temperature fluctuations, and space vacuum outside the International Space Station. Of the 2100 exposed wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds, 23% produced viable plants after return to Earth. Survival was lower in the Arabidopsis Wassilewskija ecotype and in mutants (tt4-8 and fah1-2) lacking UV screens. The highest survival occurred in tobacco (44%). Germination was delayed in seeds shielded from solar light, yet full survival w...

Why COBE and CN spectroscopy cosmic background radiation temperature measurements differ, and a remedy

Abstract: In 2004, the cosmic background radiation (CBR) temperature Tγ(CN) determined from interstellar CN absorption spectra was found to be 50 ± 20 mK higher than the COBE bolometer measured value. It was proposed that this was due, at least in part, to an error in the evaluation of the rotational components of the oscillator strengths of the rovibronic transitions corresponding to the CN B 2Σ+–X 2Σ+(0 − 0), R(0), R(1) and P(1) lines. Corrections to the standard Honl–London (HL) rotational line intensity factors used were determined. New data on interstellar CN absorption show that Tγ(CN) is 29 ± 2 mK greater than the latest value of the cosmological CBR temperature, Tγ(COBE) = 2.72548 ± 0.00057 K. These new results and CN fluorescence lifetime data are shown to give similar derived values for improved HL corrections as well as providing further evidence for the intramolecular coupling between the relevant B 2Σ+ state rotational levels and close-lying levels of the A 2Π state which invalidates the standard HL factors. Revised HL factors may be required in future Tγ(CN) measurements, in particular in high-redshift sites, which cannot be studied by bolometric means.

Ionization photophysics and Rydberg spectroscopy of diacetylene

Abstract: Photoionization of diacetylene was studied using synchrotron radiation over the range 8–24 eV, with photoelectron-photoion coincidence (PEPICO) and threshold photoelectron–photoion coincidence (TPEPICO) techniques. Mass spectra, ion yields, total and partial ionization cross-sections were measured. The adiabatic ionization energy of diacetylene was determined as IEad = (10.17 ± 0.01) eV, and the appearance energy of the principal fragment ion C4H+ as AE = (16.15 ± 0.03) eV. Calculated appearance energies of other fragment ions were used to infer aspects of dissociation pathways forming the weaker fragment ions , C3H+, and C2H+. Structured autoionization features observed in the PEPICO spectrum of diacetylene in the 11–13 eV region were assigned to vibrational components of three new Rydberg series, R1(nsσg, n = 4–11), R2(ndσg, n = 4–7) and R3(ndδg, n = 4–6) converging to the A2Πu state of the cation, and to a new series R′1(nsσg, n = 3) converging to the state of the cation. The autoionization mechanisms ...

VUV photoionization of acetamide studied by electron/ion coincidence spectroscopy in the 8-24 eV photon energy range

Abstract: A VUV photoionization study of acetamide was carried out over the 8–24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E. (1 2

Size effects on cation heats of formation. I. Methyl substitutions in nitrogenous compounds

Abstract: The heats of formation of molecular ions are often not known to better than 10 or 20 kJ/mol. The present study on nitrogenous compounds adopts the graphical approach of Holmes and Lossing [8] which relates cation heats of formation to cation size. A study of methyl substitution in formamides and acetamides is followed by an examination of heat of formation data on carbon-site and nitrogen-site methyl substitution in immonium, amine, imine, ammonium and amino cations. The results provide tests of the validity of this graphical method and also suggest investigating or re-investigating the ionization energies and the heats of formation of several of the molecules studied.

VUV spectroscopy and photochemistry of five interstellar and putative prebiotic molecules

Abstract: For many years, our group has been investigating the VUV spectroscopy and photochemistry of molecules of astrophysical (Jochims et al. a,b; Leach et al. ; Schwell et al. ) and prebiotic interest (Schwell et al. ). Polyynes and cyano-polyynes that are abundant in the interstellar medium (ISM) and in planetary atmospheres, have been investigated too (e.g. Fray et al. ). An aerosol source for reactive and thermo-labile compounds has been developed (Gaie-Levrel et al. ) to perform gas-phase measurements. These are necessary to measure intrinsic molecular properties and to compare to quantum chemical calculations. Besides measuring absolute absorption and photoionization cross sections, dissociative channels and their involved excited states are identified for a number of molecules of interstellar interest. Branching ratios of the respective elementary photoreactions are determined in order to understand and model the photochemistry occurring in the ISM. Some very recent results on the dissociative photoionization of methylformate (MF), glycolaldehyde (GA), dimethylether (DIM), aminoacetonitrile (AAC) and cyanoacetylene (CA), are presented here.