There are two HSNO conformers, cis and trans, which are approximately isoenergetic, the latter possibly slightly lower.
Low-J rotational transition frequencies with ¹⁴N hyperfine splitting are from
(1) M. Nava, M.-A. Martin-Drumel, C. A. Lopez, K. N. Crabtree, C. C. Womack, T. L. Nguyen, S. Thorwirth, C. C. Cummins, J. F. Stanton, and M. C. McCarthy, 2016, J. Am. Chem. Soc. 138, 11441.
The limited data set required D_K and d₂ to be kept fixed to values from a quantum-chemical calculation. For the same reason, the calculated spectrum was truncated at J = 10, K_a = 2 for a-type transitions and 1 for b-type transitions as well as 120 GHz. The positions of K_a = 2 transitions should be viewed with some caution. Nevertheless, the calculation should be accurate enough for searches in cold environments.
The two conformers were treated as separate molecules in the calculation of the partition function.
The dipole moment components are from a quantum-chemical calculation by
(2) S. Thorwirth, 2016, unpublished results related to (1).