Abstract
The spectrum of isocyanic acid has been examined in the photographic infra‐red using a 21‐ft. grating spectrograph and path lengths up to 500 m. The rotational structure of several bands has been analyzed and the energy levels and moments of inertia determined. With their help the coarse rotational structure of two of the fundamentals has also been analyzed. The molecular parameters fitting best our data and published electron diffraction results for the C–N and C–O bond distances are: r(H–N)=1.000A, ≰ H–N–C=125.5°.