2014ApJ...795...40C

We report the tentative detection in space of the nitrosylium ion, NO⁺. The observations were performed toward the cold dense core Barnard 1-b. The identification of the NO⁺ J = 2-1 line is supported by new laboratory measurements of NO⁺ rotational lines up to the J = 8-7 transition (953207.189 MHz), which leads to an improved set of molecular constants: B₀= 59597.1379(62) MHz, D₀= 169.428(65) kHz, and eQq₀(N) = -6.72(15) MHz. The profile of the feature assigned to NO⁺ exhibits two velocity components at 6.5 and 7.5 km/s, with column densities of 1.5x10¹² and 6.5x10¹¹/cm2, respectively. New observations of NO and HNO, also reported here, allow us to estimate the following abundance ratios: X(NO)/X(NO⁺) ≃ 511, and X(HNO)/X(NO⁺) ≃ 1. This latter value provides important constraints on the formation and destruction processes of HNO. The chemistry of NO⁺ and other related nitrogen-bearing species is investigated by the means of a time-dependent gas phase model which includes an updated chemical network according to recent experimental studies. The predicted abundance for NO⁺ and NO is found to be consistent with the observations. However, that of HNO relative to NO is too high. No satisfactory chemical paths have been found to explain the observed low abundance of HNO. HSCN and HNCS are also reported here with an abundance ratio of ≃ 1. Finally, we have searched for NNO, NO₂, HNNO⁺, and NNOH⁺, but only upper limits have been obtained for their column density, except for the latter for which we report a tentative 3σ detection.