The reactivity of Cyclopropyl cyanide in Titan's atmosphere: a possible pre-biotic mechanism E. Lopez a , D. Ascenzi b , P. Tosi b , J.M. Bofill c , J. de Andrés a , M. Albertí a , J.M. Lucas a , A. Aguilar a* a Departament de Ciència de Materials i Química Física, Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Martí i Franquès, 1, 08028 Barcelona, Spain b Dipartimento di Fisica, Università degli Studi di Trento, I-38123 Trento, Italy c Departament de Química Inorgànica i Química Orgànica, Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Martí i Franquès, 1, 08028 Barcelona, Spain *Corresponding author: Dept. Ciència de Materials i Química Física Facultat de Química Universitat de Barcelona C/ Martí i Franquès, 1 08028-Barcelona SPAIN fax: +34 93 402 12 31 e-mail: a.aguilar@ub.edu ABSTRACT Cyclopropyl cyanide and other simple nitriles detected on Titan's atmosphere could be precursors leading to the formation of organic macromolecules in the atmosphere of the largest Saturn’s satellite. Proposing a thermodynamically possible mechanism that explains their formation and supports experimental results represents a difficult challenge. Experiments done in the Atomic and Molecular Physics Laboratory at the University of Trento (AMPL), have studied the ion-molecule reaction between cyclopropyl cyanide and its protonated form, reaction products being characterized by mass spectrometr y. In addition to the expected ion- molecule adduct stabilized by non-covalent long-range interactions, in this work we prove that another distinct species having the same mass to charge ratio ( m/z) of 135 is also produced. Moreover, from a previous study of the neutral cyclopropyl cyanide potential energy surface (PES) which shows a partial biradical character it has been possible to characterize the formation through the bimolecular reaction of a new covalent cyclic organic molecule. Calculations have been carried out at the ab initio Möller-Plesset (MP2) level of 1