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[41.04] The Distribution of NO and N2O in the Sgr B2 Molecular Cloud: Evidence of High Temperature Kinetics

D. T. Halfen, A. J. Apponi, L. M. Ziurys (University of Arizona)

Observations of NO and N₂O have been conducted at 2mm towards the Sgr B2 complex using the Kitt Peak 12m telescope with a beam size of 42 arcsec. The J= 6 arrow 5 transition of N₂O and the ²Pi_1/2⁺, J= 3/2 arrow 1/2 line of NO were mapped over a 5 by 2 \arcmin area, which contained the core sources Sgr B2(N), Sgr B2(M), and Sgr B2(S). The NO emission was found to be extended over the whole region with local maximum at the cloud cores - a distribution very similar to that of HNO. In contrast, N₂O appeared to be concentrated at Sgr B2(N), where its extent was identical to a high energy transition of methanol (J_K= 14₀ arrow 14_-1 E). Because this CH₃OH line can only be excited at high temperatures, it is very likely that N₂O is formed from gas phase reactions with activation energy barriers. This observational result is supported by gas-phase kinetics. The only viable route leading to N₂O is the reaction NO + NH arrow N₂O + H, which has a strongly temperature dependent rate.

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