Context. Protoplanetary disks are vital objects in star and planet formation, possessing all the material, gas and dust, which may form a planetary system orbiting the new star. Small, simple molecules have traditionally been detected in protoplanetary disks; however, in the ALMA era, we expect the molecular inventory of protoplanetary disks to significantly increase. Aims. We investigate the synthesis of complex organic molecules (COMs) in protoplanetary disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA. Methods. We have coupled a 2D steady-state physical model of a protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs. We compare the resulting column densities with those derived from observations and perform ray-tracing calculations to predict line spectra. We compare the synthesised line intensities with current observations and determine those COMs which may be observable in nearby objects. We also compare the predicted grain-surface abundances with those derived from cometary comae observations. Results. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ∼10 −6 -10 −4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, ∼10 −12 -10 −7 . Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H 2 CO observed towards T Tauri star-disk systems. There is poor agreement with HC 3 N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH 3 OH are consistent with upper limits determined towards all sources. Our models suggest CH 3 OH should be readily observable in nearby protoplanetary disks with ALMA; however, detection of more complex species may prove challenging, even with ALMA "Full Science" capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun's natal disk.

The birth environment of the Sun will have influenced the physical and chemical structure of the pre-solar nebula, including the attainable chemical complexity reached in the disk, important for prebiotic chemistry. The formation and distribution of complex organic molecules (COMs) in a disk around a T Tauri star is investigated for two scenarios: (i) an isolated disk, and (ii) a disk irradiated externally by a nearby massive star. The chemistry is calculated along the accretion flow from the outer disk inwards using a comprehensive network which includes gas-phase reactions, gas-grain interactions, and thermal grain-surface chemistry. Two simulations are performed, one beginning with complex ices and one with simple ices only. For the isolated disk, COMs are transported without major chemical alteration into the inner disk where they thermally desorb into the gas reaching an abundance representative of the initial assumed ice abundance. For simple ices, COMs can efficiently form on grain surfaces under the conditions in the outer disk. Gas-phase COMs are released into the molecular layer via photodesorption. For the irradiated disk, complex ices are also transported inwards; however, they undergo thermal processing caused by the warmer conditions in the irradiated disk which tends to reduce their abundance along the accretion flow. For simple ices, grain-surface chemistry cannot efficiently synthesise COMs in the outer disk because the necessary grain-surface radicals, which tend to be particularly volatile, are not sufficiently abundant on the grain surfaces. Gas-phase COMs are formed in the inner region of the irradiated disk via gas-phase chemistry induced by the desorption of strongly bound molecules such as methanol; hence, the abundances are not representative of the initial molecular abundances injected into the outer disk. These results suggest that the composition of comets formed in isolated disks may differ from those formed in externally irradiated disks with the latter composed of more simple ices.

Methanol is ubiquitous in star-forming regions, and has recently been detected in a protoplanetary disk. Astrochemical models have shown that methanol photolysis contributes to complex organic chemistry in interstellar ices. While some methanol photolysis branching ratios have been measured, infrared condensed-phase measurements rely on assumptions about the chemistry, and mass spectrometric measurements cannot distinguish structural isomers. To address these challenges, we are using pure rotational spectroscopy to quantitatively probe the methanol photolysis products. We use a VUV laser to dissociate methanol in the throat of a supersonic expansion, and probe the products downstream after cooling is complete. We then use a rotational diagram analysis to determine the relative density of each product relative to methanol. We have detected the methoxy, hydroxymethyl, and formaldehyde photolysis products. We present here the experimental setup and the initial results and discuss these results in the context of interstellar chemistry.

Cosmic ice analogue experiments are an important aspect of astrochemistry because they help researchers construct the chemical pathways leading to molecules found in young stellar objects, comets, and meteorites. Decades of cosmic ice experiments have demonstrated the formation of various organics and how ice composition is affected by UV photons and temperature. The ice chemistry can be challenging to elucidate, and structure-specific techniques are required to uniquely identify products. We present the Sublimation Laboratory Ice Millimeter/submillimeter Experiment (SubLIME), which uses rotational spectroscopy to complement previous laboratory ice studies. Using this technique, we can detect a wide range of products, including structural and conformational isomers, of UV-photolyzed ice samples from a single spectrum. Furthermore, this technique can be used to model the observational spectra of pre-and protostellar cores and cometary comae. We will present the SubLIME setup and new spectroscopic results of sublimated UV-photolyzed ice samples containing water (H 2 O) and carbon monoxide (CO).

The process of star formation provides a rich environment for complex interstellar chemistry to occur. We are able to probe the physical and chemical processes of star and planet forming regions in detail using high resolution millimeter wave interferometry. We have used the Northern Extended Millimeter Array (NOEMA) to conduct observations of complex organic molecules (COMs) within the W3 star forming region at selected frequencies in the λ=2 mm band. W3 is a binary system with two high-mass hot cores centered on masers, W3(OH) and W3(H2O). The two cores display different chemistry despite being formed from the same interstellar cloud. This difference in chemistry may arise either because of a difference in source age, or because of different physical conditions within the sources. Interferometric observations of molecules in this region allow us to disentangle the spatial distribution of COMs and investigate the drivers of chemical differentiation between the two star-forming cores. Our results show the chemical morphology of prebiotically relevant molecules such as methanol, methyl formate, methyl cyanide, and formaldehyde, as well as kinematics and temperature distributions within the W3 complex. We will report on these findings and discuss the results in the context of interstellar prebiotic chemistry.