Microwave spectrum of the NCO radical

The rotational spectrum of the linear triatomic radical NCO has been observed by means of a Stark modulated microwave spectrometer. The NCO radical was produced by mixing HNCO with the products of a microwave discharge in CF₄. The observed rotational transitions J =52←32 role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{J =}\text{5}\text{2}\text{←}\text{3}\text{2}$$\text{J =}\text{5}\text{2}\text{←}\text{3}\text{2}$, and 72←52 role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{7}\text{2}\text{←}\text{5}\text{2}$$\text{7}\text{2}\text{←}\text{5}\text{2}$ in the 2Π32 role=presentation style=font-size: 90%; display: inline-block; position: relative;>${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ state and J =52←32 role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{J =}\text{5}\text{2}\text{←}\text{3}\text{2}$$\text{J =}\text{5}\text{2}\text{←}\text{3}\text{2}$ in the 2Π12 role=presentation style=font-size: 90%; display: inline-block; position: relative;>${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ state have been analyzed by using Hougen's formulation for a linear triatomic molecule in a ²Π state. The rotational constant, the centrifugal distortion constant, the Λ-type doubling constant, the hyperfine constants and the dipole moment have been determined. Consideration of the Λ-type doubling constant leads to the conclusion that the upper electronic state perturbing the ²Π state is A (2Σ+) role=presentation style=font-size: 90%; display: inline-block; position: relative;>$\text{A (}{}^2\text{Σ}{}^{\mathrm{+}}\text{)}$$\text{A (}{}^2\text{Σ}{}^{\mathrm{+}}\text{)}$.