Conformer-Specific Desorption in Propanol Ices Probed by Chirped-Pulse Millimeter-Wave Rotational Spectroscopy

Wepresent a new technique for the detection of molecules desorbedfrom an ice surface using broad-band millimeter-wave rotational spectroscopy.The approach permits interrogation of molecules that have undergonethe slow warmup process of temperature-programmed desorption (TPD),analogous to the warmup phase of icy grains in the interstellar mediumas they approach the central protostar. The detection is conformer-and isomer-specific and quantitative, as afforded by chirped-pulserotational spectroscopy. To achieve this, we combine ice TPD withbuffer gas cooling, followed by detection in the millimeter-wave regime.In this report we examine the TPD profiles of n-and i-propanol, the former of which may be in fivedifferent conformational isomeric forms, and which display distinctdesorption profiles. The limited conformational isomerization andtemperature-dependent relative yields of n-propanolconformers observed show that the desorption is highly conformer-specific.