Methanetetrol and the final frontier in ortho acids.

The rapid dissociation of methanetetrol (C(OH)) has been suggested as an impediment to its observation, despite the stability of its substituted derivative orthocarbonates (C(OR)). Here, the tunability of synchrotron-generated vacuum ultraviolet light and the sensitivity of photoionization are exploited to probe the exotic chemistry of the interstellar medium toward the discovery of this molecule. Laboratory-made model ices simulate the composition of astrophysical ices under conditions mimicking those found in dense interstellar molecular clouds with low temperature (5-10 K) and low pressure (<10Torr). High-energy irradiation simulates secondary electrons produced by galactic cosmic rays, one of few sources of energy that penetrate to the icy cloud interior. The reaction mechanism that yields methanetetrol is conclusively revealed by the simultaneous production and detection of key intermediates: carbonic acid (HOCOOH) and the recently reported methanetriol. State-of-the-art electronic structure calculations support the experimental observations and results suggest that if carbonic acid is sufficiently abundant in space, then methanetetrol may be waiting to be observed. The detection of methanetetrol in space-simulation experiments demonstrates that the interstellar medium is host to an unanticipated and counterintuitive chemistry that demands scientific attention.