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

A systematic study of the high-resolution spectrum of (13)C(2)H(2) in the 3microm spectral region shows Q branch features in five hot parallel bands. These bands are due to the nu(3)+nu(4) (Pi(u))<--nu(4) (Pi(g)), nu(3)+nu(5) (Pi(g))<--nu(5)(Pi(u)), nu(3)+2nu(4) (Delta(u))<--2nu(4)(Delta(g)), nu(3)+2nu(5) (Delta(u))<--2nu(5)(Delta(g)) and nu(3)+nu(4)+nu(5)(Delta(g))<--nu(4)+nu(5)(Delta(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 Delta-Delta hot bands, in the FTIR spectrum of (13)C(2)H(2).