Structure and spectroscopic properties of low-lying states of the HOC(O)O radical

The HOC(O)O radical is a product of the reaction of HOCO radicals with oxygen atoms. The present study provides theoretical prediction of critical spectroscopic features of this radical that should aid in its experimental characterization. Energies, structures, rotational constants, and harmonic frequencies are presented for the ground and two low-lying excited electronic states of HOC(O)O. The energies for the A ∼ 2 A ″ → X ∼ 2 A ′ and B ∼ 2 A ′ → X ∼ 2 A ′ electronic transitions are reported. The band origin of the B ∼ → X ∼ transition of HOC(O)O is predicted to occur in the near infrared region of the spectrum at around 1.5 eV and it is suggested to be the most promising one for observing this radical spectroscopically. The structural and spectroscopic similarities between HOC(O)O and the isoelectronic radical FC(O)O are discussed. The abundance of experimental data on the FC(O)O radical should guide the spectroscopic characterization of HOC(O)O and serve as a benchmark for the structural and spectroscopic parameters obtained from theory.