Search

Carbonyls are among the most abundant volatile organic compounds in the atmosphere. They are central to atmospheric photochemistry as absorption of near-UV radiation by the C=O chromophore can lead to photolysis. If photolysis does not occur on electronic excited states, non-radiative relaxation to the ground state will form carbonyls with extremely high internal energy. These “hot” molecules can access a range of ground state reactions. Up to nine potential ground state reactions are investigated at the B2GP-PLYP-D3/def2-TZVP level of theory for a dataset of 20 representative carbonyls. Almost all are energetically accessible under tropospheric conditions. Comparison with experiment suggests the most significant ground state dissociation pathways will be concerted triple fragmentation in saturated aldehydes, Norrish type III dissociation to form another carbonyl, and H2-loss involving the formyl H atom in aldehydes. Tautomerisation, leading to more reactive unsaturated species, is also predicted to be energetically accessible and is likely to be important when there is no low-energy ground state dissociation pathway, for example in α,β-unsaturated carbonyls and some ketones. The concerted triple fragmentation and H2-loss pathways have immediate atmospheric implication to global H2 production and tautomerisaton has implication to the atmospheric production of organic acids.

Phosphine is now well established as a biosignature, which has risen to prominence with its recent tentative detection on Venus. To follow up this discovery and related future exoplanet biosignature detections, it is important to spectroscopically detect the presence of phosphorus-bearing atmospheric molecules that could be involved in the chemical networks producing, destroying or reacting with phosphine. We start by enumerating phosphorus-bearing molecules (P-molecules) that could potentially be detected spectroscopically in planetary atmospheres and collecting all available spectral data. Gaseous P-molecules are rare, with speciation information scarce. Very few molecules have high accuracy spectral data from experiment or theory; instead, the best available data is from the RASCALL approach and obtained using functional group theory. Here, we present a high-throughput approach utilising established computational quantum chemistry methods (CQC) to produce a database of approximate infrared spectra for 958 P-molecules. These data are of interest for astronomy and astrochemistry (importantly identifying potential ambiguities in molecular assignments), improving RASCALL's underlying data, big data spectral analysis and future machine learning applications. However, this data will probably not be sufficiently accurate for secure experimental detections of specific molecules within complex gaseous mixtures in laboratory or astronomy settings., 36 pages, 10 figures