Q branch features in the hot parallel bands of 13C 2H 2 in the three micron region

Abstract

A systematic study of the high-resolution spectrum of 13C 2H 2 in the 3 μm spectral region shows Q branch features in five hot parallel bands. These bands are due to the ν 3 + ν 4 ( Π u) ← ν 4 ( Π g), ν 3 + ν 5 ( Π g) ← ν 5( Π u), ν 3 + 2 ν 4 (Δ u) ← 2 ν 4(Δ g), ν 3 + 2 ν 5 (Δ u) ← 2 ν 5(Δ g) and ν 3 + ν 4 + ν 5(Δ g) ← ν 4 + ν 5(Δ u) transitions. Sub-Q-branches ( Q e← f and Q f← 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 13C 2H 2.