The singlet and triplet states of HF2+: a theoretical study

We study the singlet and triplet states of HF2+ at the B3LYP, BHandH, BHandHLYP, MP2, MP3, MP4 and QCISD(T) levels of theory with the 6-311++G(2DF,2PD) basis set. We report geometries, vibrational frequencies and vertical excitation energies. We find that the ground state of HF2+ is the Cs HFF+ singlet with r(F–F) = 1.444, r(H–F) = 0.980 Å and α=101.96°; ω1=857, ω2=1145 and ω3=3320 cm−1. For the triplet state, there are two stable structures: the Cs HFF+ triplet (Te=0.79 eV) with r(F–F) = 1.799, r(H–F) = 0.962 Å and α=102.53°; ω1=543, ω2=734 and ω3=3530 cm−1 and the C∞v FHF+ triplet (Te=0.92 eV) with r(H–F) = 1.179 Å; ω1=544, ω2=900 and ω3=1418 cm−1.