Analytical study of level crossings in the Stark-Zeeman spectrum of ground state OH Nathan Cawley, Zachary Howard, Michaela Kleinert and Mishkatul Bhattacharya Eur. Phys. J. D, 67 11 (2013) 233 Published online: 15 November 2013 DOI: 10.1140/epjd/e2013-40462-1