Heavy atom nitroxyl radicals. VI. The electronic spectrum of jetcooled H2PO, the prototypical phosphoryl free radical

The previously unknown electronic spectrum of the H2PO free radical has been identified in the 407–337 nm region using a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio predictions of the properties of the ground and first two excited doublet states were used to identify the spectral region in which to search for the electronic transition and were used to aid in the analysis of the data. The band system is assigned as the B2A−X2A electronic transition which involves promotion of an electron from the π to the π* molecular orbital. The excited state r0 molecular structure was determined by rotational analysis of high resolution LIF spectra to be r(PO) = 1.6710(2) Å, r(PH) = 1.4280(6) Å, θ(HPO) = 105.68(7)◦, θ(HPH)= 93.3(2)◦, and the out-of-plane angle = 66.8(2)◦. The structural changes on electronic excitation, which include substantial increases in the PO bond length and out-of-plane angle, are as expected based on molecular orbital theory and our previous studies of the isoelectronic H2AsO, Cl2PS, and F2PS free radicals.