Photodissociation and chemistry of N2 in the circumstellar envelope of carbon-rich AGB stars Xiaohu Li, Tom J. Millar, Catherine Walsh, Alan N. Heays and Ewine F. van Dishoeck A&A, 568 (2014) A111 Published online: 01 September 2014 DOI: 10.1051/0004-6361/201424076