A molecule with small rotational constants containing an atom with a large nuclear quadrupole moment: The microwave spectrum of trans-1-iodoperfluoropropane

Using pulsed jet chirped-pulse, and cavity-based Fourier transform microwave spectroscopies over 900 transitions have been recorded for the title molecule in the 1-4 GHz and 8-18 GHz regions. The C₁, C₂ and C₃ carbon-13 species have been observed in natural abundance allowing a substitution structure for the CCC backbone to be determined. Nearly all the transitions observed were either a-type R branches or b-type Q branches. No c-type transitions were observed consistent with only the trans conformer being present under our experimental conditions. The χ_aa, χ_bb, χ_cc and χ_ab components of the iodine nuclear quadrupole coupling tensor have been determined. Of note, several forbidden, Δ J ± 2 transitions, and one Δ J ± 3 transition were observed with quite reasonable intensity. These observations have been rationalized through considerations of near degeneracies between energy levels connected via a large χ_ab value (≈1 GHz).