D. G. Horne

Bio: D. G. Horne is an academic researcher from University of Cambridge. The author has contributed to research in topics: Flash photolysis & Radical. The author has an hindex of 1, co-authored 1 publications receiving 15 citations.

The photolysis of acyclic azines and the electronic spectra of R1R2CN • radicals

Abstract: Flash photolysis of formaldazine, acetaldazine and dimethylketazine produced three new transient u.v. spectra which have been attributed to the CH 2 N., CH 3 CHN. and (CH 3 ) 2 CN. free radicals. The absolute rate constant for the second-order decay of the CH 2 N • radical has been determined. The pressure dependence of the product quantum yields from the continuous 253.7 nm photolysis of acetaldazine was investigated. The results from these experiments, and a re-interpretation of the data published by Brinton on acetaldazine photolysis, have been used to derive a free radical mechanism which includes several primary reactions, of which NN fission is the major process under all experimental conditions, and a sequence of secondary reactions in which the disproportionation of CH 3 CHN. radicals predominates. The overall mechanism satisfactorily describes the pressure and wavelength dependence of acetaldazine photolysis. Preliminary experiments on formaldazine indicate that the photolysis of the azine proceeds by a very similar mechanism.

A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres

Abstract: There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect life and prebiotic chemistry outside the solar system. We present an ion-neutral chemical network constructed from scratch, Stand2015, that treats hydrogen, nitrogen, carbon and oxygen chemistry accurately within a temperature range between 100 K and 30000 K. Formation pathways for glycine and other organic molecules are included. The network is complete up to H6C2N2O3. Stand2015 is successfully tested against atmospheric chemistry models for HD209458b, Jupiter and the present-day Earth using a simple 1D photochemistry/diffusion code. Our results for the early Earth agree with those of Kasting (1993) for CO2, H2, CO and O2, but do not agree for water and atomic oxygen. We use the network to simulate an experiment where varied chemical initial conditions are irradiated by UV light. The result from our simulation is that more glycine is produced when more ammonia and methane is present. Very little glycine is produced in the absence of any molecular nitrogen and oxygen. This suggests that production of glycine is inhibited if a gas is too strongly reducing. Possible applications and limitations of the chemical kinetics network are also discussed.

A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres

Abstract: There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect life and prebiotic chemistry outside the solar system. We present an ion-neutral chemical network constructed from scratch, Stand2015, that treats hydrogen, nitrogen, carbon and oxygen chemistry accurately within a temperature range between 100 K and 30000 K. Formation pathways for glycine and other organic molecules are included. The network is complete up to H6C2N2O3. Stand2015 is successfully tested against atmospheric chemistry models for HD209458b, Jupiter and the present-day Earth using a simple 1D photochemistry/diffusion code. Our results for the early Earth agree with those of Kasting (1993) for CO2, H2, CO and O2, but do not agree for water and atomic oxygen. We use the network to simulate an experiment where varied chemical initial conditions are irradiated by UV light. The result from our simulation is that more glycine is produced when more ammonia and methane is present. Very little glycine is produced in the absence of any molecular nitrogen and oxygen. This suggests that production of glycine is inhibited if a gas is too strongly reducing. Possible applications and limitations of the chemical kinetics network are also discussed.

On the abundance of non-cometary HCN on Jupiter

Abstract: Using one-dimensional thermochemical/photochemical kinetics and transport models, we examine the chemistry of nitrogen-bearing species in the Jovian troposphere in an attempt to explain the low observational upper limit for HCN. We track the dominant mechanisms for interconversion of N2–NH3 and HCN–NH3 in the deep, high-temperature troposphere and predict the rate-limiting step for the quenching of HCN at cooler tropospheric altitudes. Consistent with some other investigations that were based solely on time-scale arguments, our models suggest that transport-induced quenching of thermochemically derived HCN leads to very small predicted mole fractions of hydrogen cyanide in Jupiter's upper troposphere. By the same token, photochemical production of HCN is ineffective in Jupiter's troposphere: CH4–NH3 coupling is inhibited by the physical separation of the CH4 photolysis region in the upper stratosphere from the NH3 photolysis and condensation region in the troposphere, and C2H2–NH3 coupling is inhibited by the low tropospheric abundance of C2H2. The upper limits from infrared and submillimetre observations can be used to place constraints on the production of HCN and other species from lightning and thundershock sources.