The deep 3.4 μm interstellar absorption feature toward the IRAS 18511+0146 cluster M. Godard, T. R. Geballe, E. Dartois and G. M. Muñoz Caro A&A, 537 (2012) A27 Published online: 22 December 2011 DOI: 10.1051/0004-6361/201117197