Sorbonne Universités, Université Pierre et Marie Curie, UPMC Univ Paris 06, CNRS, UMR 8233, MONARIS, Paris, France Reactions of ground state nitrogen atoms N( 4 S) with astrochemical-relevant molecules on interstellar dusts. Sendres Nourry, Lahouari Krim

In the core of dense molecular clouds, N 2 is predicted to form efficiently at 10K N + M Product Reactions in solid phase at low temperatures under non-energetic conditions laboratory investigations carried out at relatively higher temperatures between 296 and 56 K in gas phase. N + CN N 2 + C N + NO N 2 + O Y.P. Viala,1986. Chemical equilibrium from diffuse to dense interstellar clouds. I. Galactic molecular clouds. Astron Astrophys Suppl Ser 64, 391 J. Daranlot, U. Hincelin, A. Bergeat, M. Costes, J.-C. Loison, V. Wakelam, K. M. Hickson, Elemental nitrogen partitioning in dense interstellar clouds. 109, 10233

N( 2 D) + M N( 2 P) + M Products N( 4 S) + M (160 kcal/mol). N( 2 D) + CH 3 OH → CH 2 OH + NH (1) N( 2 D) + CH 3 OH → CH 3 O + NH (2) N( 2 D) + CH 3 OH → CH 3 + HNO (3) Reactivity of ground state nitrogen atoms radical with CH 3 OH 0 eV 2.38 eV 3.57 eV

IR N/N 2 10 K N( 4 S) bombardment of CH 3 OH ice CH 3 OH IR 10 K

N + CH 3 OH → CH 3 + HNO CH 3 ? HNO ?

N/N 2 10 K CH 3 OH Solid N 2 CH 3 OH CH 3 OH desorption

N 2 + NN3N3 CH 3 OH + NH 2 CO

But at 10K the N + CH 3 OH reaction is complete ! N/N 2 CH 3 OH 10 K IR N/N 2 10 K CH 3 OH Bombardment of methanol ice by N atoms at 10 K Co-injection of CH 3 OH and N atoms at 10 K

N/N 2 CH 3 OH 3 K IR Dark reaction 3 K Heating at 10K 3-10 K N2(X1Σg+)N2(X1Σg+) 0 eV N2(A3Σu+)N2(A3Σu+) 9.2 eV 0.6 ms N( 2 D) N( 4 S)0 eV 2.4 eV 40 s Lifetime of N( 2 D) and N 2 ( A 3 Σ u + ) metastable excited nitrogen species

CH 3 O Sample deposition and 2h dark reaction CH 3 OH + N at 3K 3K 8K 9K 10K 11K 3K 8K 9K 10K 11K HCO H 2 CO 3K 8K 9K 10K 11K CH 2 OH CH 3 OH CH 2 OH/CH 3 O HCO

N( 2 D) N( 2 P) N( 4 S) 0 eV 2.38 eV 3.57 eV 1eV=96 kJ/mol~100kJ/mol Simplified energy diagram of N 2 R NN (Å) Simplified diagram of atomic nitrogen N( 4 S) + N( 4 S) → N 2 (A) Metastable can retain a high energy of 6.2 ev

N( 4 S) + N( 4 S) → N 2 (A) Solid N 2 [CH 3 OH]/[N]/[N 2 ] = 0.2/8/100 N N N N CH 3 OH N 2 (A) + N( 4 S) → N 2 (X) + N( 2 P) N 2 (A) + N( 4 S) → N 2 (X) + N( 2 D) (2) (3) J L Jauberteau et al New Journal of Physics 4 (2002) 39.1 (2) Kajihara et al Chemical physics 186 ( 1994) 395 N2N2 N ( 2 D/ 2 P) + CH 3 OH → CH 2 OH/CH 3 O → H 2 CO → HCO N 2 (A) + CH 3 OH → CH 2 OH/CH 3 O → H 2 CO → HCO

N( 4 S) + N( 4 S) N 2 (A) N( 2 P) and N( 2 D) Hydrogen atom abstraction reactions Between 3 and 10 K These results underline the problem of the low chemical stability of some species formed and destroyed in dense clouds without any contribution of cosmic-ray particles or high energy photons

2 nd year UPMC Graduate Student € Sendres Nourry