High resolution Raman spectroscopy of gases with laser sources. XI. The spectrum of cyanogen

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Abstract
The pure rotational and rotation–vibrational Raman spectra of cyanogen, C2N2, were photographed under high resolution. The spectra were excited with a single mode argon laser operating at λ=4880 Å. The pure rotation spectrum shows a partially resolved hot band structure that is assigned to the ν5 1 and 2ν5 vibrationally excited states. The l‐type doubling in the pure rotational spectrum of molecules in the ν1 5 state is sufficiently well resolved at high J values to allow a determination of the l‐type doubling constant. The ν1(Σ+ g ) and ν1 4(Π g ) fundamental rotation–vibration bands were also photographed. Both fundamentals are overlapped by vibrational hot bands originating in low‐lying vibrational levels. Molecular constants obtained in the present work are, in units of cm−1, The constants for the ν1 5 and 2ν5 0,2 states were obtained from the pure rotation spectrum. The vibrational constants were found to be The ground state constants B 0 and D 0 and their uncertainties were determined by an extrapolation procedure. For all other constants the quoted errors are one standard deviation and only represent the internal errors generated in the least squares analysis of the data. Vibrational constants determined from Q‐branch measurements only are indicated by (Q).