Q branch features in the hot parallel bands of 13C2H2 in the three micron region

A systematic study of the high-resolution spectrum of 13C2H2 in the 3 μm spectral region shows Q branch features in five hot parallel bands. These bands are due to the ν3 + ν4 (Πu) ← ν4 (Πg), ν3 + ν5 (Πg) ← ν5(Πu), ν3 + 2ν4 (Δu) ← 2ν4(Δg), ν3 + 2ν5 (Δu) ← 2ν5(Δg) and ν3 + ν4 + ν5(Δg) ← ν4 + ν5(Δu) transitions. Sub-Q-branches (Qe←f and Qf←e)are found to be resolved in the first three hot bands. More than 70 Q branch lines have been assigned, spread over the five hot bands. We have applied separate linear least squares fit to the transition wavenumbers of each Q branch/sub-Q-branches, which have yielded values of band origins and rotational constants, in agreement with those derived from the analysis of the P and R branches in earlier work. The analysis of the sub-Q-branches have also provided values of the l-doubling constants. This is the first report on the observation of Q branch lines in Δ−Δ hot bands, in the FTIR spectrum of 13C2H2.