Spectroscopic characterization and detection of Ethyl Mercaptan in Orion
  New laboratory data of ethyl mercaptan, CH$_{3}$CH$_{2}$SH, in the millimeter and submillimeter-wave domains (up to 880 GHz) provided very precise values of the spectroscopic constants that allowed the detection of $gauche$-CH$_3$CH$_2$SH towards Orion KL. 77 unblended or slightly blended lines plus no missing transitions in the range 80-280 GHz support this identification. A detection of methyl mercaptan, CH$_{3}$SH, in the spectral survey of Orion KL is reported as well. Our column density results indicate that methyl mercaptan is $\simeq$ 5 times more abundant than ethyl mercaptan in the hot core of Orion KL. 
L. Kolesnikov\'a, B. Tercero, J. Cernicharo, J. L. Alonso, A. M. Daly,   B. P. Gordon and S. T. Shipman
astro-ph.GA