Λ-Doubling in the v = 2 ← 0 overtone band in the infrared spectrum of NO

Λ-doubling in the first overtone, v = 2 ← 0, vibration-rotation band of ¹⁴N¹⁶O has been measured with Doppler-limited resolution using a tunable difference-frequency laser spectrometer. P- and R-branch Λ-splittings for $\text{1}\text{2}\text{<- J ≤}\text{53}\text{2}$ in the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ electronic state and for $\text{47}\text{2}\text{≤ J ≤}\text{57}\text{2}$ in the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ state have been determined by least squares fitting of the spectral profiles to Gaussian doublets with a precision of better than ±1.5 MHz for the stronger, well-resolved lines. The Λ-doubling parameters obtained from a least square Hamiltonian analysis of the data for the v = 2 level are p₂ = 349.542 (60) MHz and q₂ = 2.754 (5) MHz with the error limits representing three standard deviations. These precise v = 2 parameters are combined with excellent v = 1 constants available in the literature to calculate the Λ-splittings expected in the v = 2 ← 1 hot band of NO for comparison with recently reported measurements. The effect of nuclear hyperfine structure on the lineshapes of some of the low J overtone transitions has also been observed.