Investigating The "minimum Energy Principle" In Searches For New Molecular Species - The Case Of H2c3o Isomers

Next generation interferometers offer new possibilities of extracting information about the history and conditions of interstellar regions through analysis of molecular abundance ratios, which act as chemical fingerprints. To fully utilize these new capabilities, however, complete molecular inventories of interstellar regions must be established and the relative contributions of different chemical processes must be determined. Current theories on molecule formation will therefore be guiding forces in future observing strategies. Recently, Lattelais et al. have interpreted aggregated observations of molecular isomers to suggest that there exists a “minimum energy principle”, such that molecular formation will favor more stable molecular isomers for thermodynamic reasons. To test the predictive use of this model, we have fully characterized the spectra of the three isomers of C$_3$H$_2$O toward the well known molecular region Sgr B2. Evidence for the detection of the isomers cyclopropenone (c-C$_3$H$_2$O) and propynal (HCCCHO) is presented, along with evidence for the non-detection of the lowest zero-point energy isomer, propadienone (CH$_2$CCO). We interpret these observations as evidence that chemical formation pathways, which may be under kinetic control, have a more pronounced effect on final isomer abundances than thermodynamic effects such as the minimum energy principle (Lattelais et al. 2009, ApJ 696, L133). These results suggest that as ALMA opens up new space for molecular discovery, focus should be placed on molecules and molecular reactions under kinetic control, and we briefly discuss the possible applications of isomeric analysis in the era of broadband interferometry