Highlights

Abstract

Graphical abstract

Keywords

۱٫ Introduction

۲٫ Apparatus

۳٫ Buffer gas cooling considerations

۳٫۱٫ Buffer gas cell & pumping requirements

۳٫۲٫ Diffusion and cooling times

۳٫۳٫ Buffer gas loading of sublimed molecules

۴٫ Spectrometer sensitivity

۵٫ Conclusion

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

References

Abstract

High temperatures and associated poor rotational partition functions have hindered the application of high-resolution rotational spectroscopy for detection of molecules desorbing from an ice substrate. Here, an experimental approach is presented which will enable such investigations through incorporation of a buffer gas cooling cell. We discuss design considerations for this apparatus and the expected performance based upon OC34S measurements made with a related spectrometer in a 14.7 K sampled uniform flow. We highlight specific applications of this technique including chiral sensing of molecules generated in an interstellar ice, and the synthesis of exotic species not amenable to generation in the gas-phase.

I. Introduction

Chemistry taking place in ices profoundly impacts atmospheric chemistry and chemistry in astrochemical environments[1,2]. For example, the synthesis of prebiotic amino acids and sugars, as well as the enantiomeric excess observed on Earth may be attributed to chemistry that took place in ice[3,4]. However, current laboratory studies mainly employ mass spectrometric and Fourier-transform infrared spectroscopic detection and do not take advantage of recent tremendous advances of broadband rotational spectroscopy[5,6]. This is largely because of the disadvantage of the rotational partition function associated with molecules desorbing from these ices at typical temperatures from 80-200 K. A means to cool these molecules offers the advantage of rotational spectroscopy for effective probes of chirality, isomer-specificity, complex mixture analysis, and meaningful relative intensities for product branching ratios. There have been, to our knowledge, two reports on the application of millimeter and submillimeter spectroscopy applied to study interstellar ice chemistry. Widicus-Weaver et al. demonstrated the first such experiments in their detection of thermally desorbed H2O, D2O, and CH3OH originating in a solid film created at ~ 12K[7].