Far infrared laser magnetic resonance detection of NH and ND (a ¹Δ)

Rotational spectra of the excited a ¹Δ state of NH and ND have been observed by far infrared laser magnetic resonance spectroscopy. For ND(a ¹Δ) the spectroscopic constants are B₀ = 264 750.263(30) MHz, D₀ = 14.383 83(91) MHz, a_N = 109.63(22) MHz, a_D = 11.03(23) MHz, eqQ(N) = -4.0(15) MHz, gr = -0.000 86(10), and g_L = 1.000 506(17). For NH (a ¹Δ), the constants are B₀ = 493 043.182(95) MHz, D₀ = 50.453 MHz (constrained in fit), a_N = 109.65(85) MHz, a_H = 70.9(14) MHz, eqQ(N) = -4.0 MHz (constrained in fit), g_r = -0.001 58(6), and g_L = 1.001 03 (constrained in fit). Aspects of the electronic structure of the radical as revealed by the magnetic hyperfine constants are discussed in relation to those of chemically similar systems. The Zeeman parameters are interpreted in terms of mixing of the a ¹Δ state with the c ¹Π state.