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This second paper in a series of two describes the chirped-pulse ice apparatus that permits the detection of buffer gas cooled molecules desorbed from an energetically processed ice using broadband mm-wave rotational spectroscopy. Here, we detail the lower ice stage developed to generate ices at 4 K, which can then undergo energetic processing via UV/VUV photons or high-energy electrons and which ultimately enter the gas phase via temperature-programmed desorption (TPD). Over the course of TPD, the lower ice stage is interfaced with a buffer gas cooling cell that allows for sensitive detection via chirped-pulse rotational spectroscopy in the 60–90 GHz regime. In addition to a detailed description of the ice component of this apparatus, we show proof-of-principle experiments demonstrating the detection of H2CO products formed through irradiation of neat methanol ices or 1:1 CO + CH4 mixed ices.
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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 ∼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 ∼56 K, which is much lower than their sublimation temperature of 170 K.
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- Award ID(s):
- 2314347
- PAR ID:
- 10515840
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- ACS Earth and Space Chemistry
- Volume:
- 8
- Issue:
- 1
- ISSN:
- 2472-3452
- Page Range / eLocation ID:
- 14 to 20
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsearthspacechem.3c00332
