The water adducts of triacetone triperoxide (TATP) have been observed by using broadband rotational spectroscopy. This work opens a new way for the gas-phase detection of this improvised explosive. The observed clusters exhibit unusual water dynamics and rarely observed multicenter interactions. TATP-H2O is formed from the D3 symmetry conformer of TATP with water lying close to the C3 axis. Water rotation around this axis with a very low barrier gives rise to the rotational spectrum of a symmetric top. The main interaction of the monohydrate is a four-center trifurcated donor Ow-H⋅⋅⋅O hydrogen bond, not observed previously in the gas phase, reinforced by a weak four-center trifurcated acceptor C−H⋅⋅⋅Ow interaction. Surprisingly, all structural signatures show the weakness of these interactions. The complex TATP-(H2O)2 is formed from the monohydrated TATP by the self-association of water.
