Submillimeter spectrum and analysis of vibrational and hyperfine coupling effects in (HI)2

Observed rotational–vibrational transitions of HI dimer in the geared bending mode, centered at 511.9 GHz, are reported. This ∼50 kHz spectrum was recorded using a co-axially configured pulsed jet submillimeter spectrometer and hyperfine structure of R(J) and P(J) transitions from the quadrupole moments of iodine nuclei are completely resolved for low-J transitions. Analysis of hyperfine patterns was carried out using a theoretical approach accounting for the large amplitude motion effects and hyperfine matrix elements within and between vibrational states. The submillimeter analysis is consistent with a vibrationally averaged ground state Rcm = 4.56372(1) Å and average bending angle θ = 46.405(1)°.