First detection of [N II] 205 μm absorption in interstellar gas. Herschel-HIFI observations towards W 31C, W 49N, W 51, and G34.3+0.1
Journal article published in 2014 by
C.~M Persson,
M. Gerin,
B. Mookerjea,
J.~H Black,
M. Olberg,
J.~R Goicoechea,
G.~E Hassel,
E. Falgarone,
F. Levrier,
K.~M Menten,
J. Pety 
