Conformer Distributions of n-Propyl Cyanide in the Gas Phase and Following Ice Sublimation Measured by Broadband Rotational Spectroscopy

The conformer distribution of normal-propyl cyanide is investigated using broadband chirped pulse rotational spectroscopy in the millimeter-wave regime coupled with buffer gas cooling. Here we explore the relative abundances of the anti and gauche conformers following room-temperature gas-phase injection into a 25 K buffer gas cell and compare to that which is observed following temperature programmed desorption from an ice surface, similar to the slow warm-up experienced by ice grains as they approach warmer regions within the interstellar medium. The conformer distributions observed in the gas phase from room temperature injection are then used to determine their relative energies, an important parameter needed to interpret the isomer and conformer abundances derived from astronomical observations. We find the gauche conformer to be the most stable species by similar to 97 +/- 21 cm(-1). We further examine the relative conformer abundances following ice desorption, which are distinct from those following the gas-phase introduction. The ratios measured off the ice correspond to a conformer temperature of similar to 56 K, which is much lower than their sublimation temperature of 170 K.