In this talk I will cover three topics. First, I will present some recent highlights from ALMA related to astrochemistry. Second, I will describe some of the challenges inherent in analyzing ALMA spectroscopic data, using as an illustrative template observations of NGC6334I - a cluster of forming massive protostars. Finally, I will give an overview of approved and future ALMA development projects that promise to open new windows for molecular spectroscopic study with ALMA.

Quantitative spectrometry is a primary source for determination of composition as well as physical properties of planetary atmospheres, including the Earth’s and exo-planetary atmospheres. NASAs charter to explore the universe, the solar system, and to observe Earth from space results in several different challenges for molecular spectroscopy, including: (1) a desire for comprehensive spectral databases; (2) extreme physical characterizations of bulk atmospheric gases; (3) characterization of transient molecules; (4) development of sensors for extraterrestrial deployment. Along with colleagues across the world, the molecular spectroscopy laboratory at NASAs Jet Propulsion Laboratory works towards these goals, providing both critical information for specific missions as well as general knowledge to support a broad community of planetary scientists, astronomers, and Earth scientists. This presentation will show examples in each challenging area with highlights for spectral characterization efforts to support the Herschel/HIFI and Cassini missions, high-pressure spectroscopy to support the OCO missions and exoplanet research, characterizations of radical and ion species, as well as the development of miniaturized cavity spectrometers that may enable molecular and enantiomeric specific detections in-situ.

The roles that polycyclic aromatic hydrocarbons (PAHs) play in the interstellar medium (ISM) are thought to be quite diverse, from ice grain interactions to hydrogen production. Because of the importance that these roles would have in the ISM, we are interested in using structural information obtained via microwave spectroscopy to disentangle the first interactions between PAHs and astronomically relevant molecules. To do this, we have used chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy to investigate PAHs clustered with astronomical constituents, such as water. The PAHs vary in size and aromaticity, creating different preferred binding motifs of the clustered molecule(s). By using isotopic data (either measured in natural abundance or through isotopically enriched samples) exact structural data has been gathered. A comparison of these systems will be presented with an in depth look at the different binding interactions present in each cluster and their binding motifs.

Fourier transform spectroscopy (FTS) based on optical frequency combs offers a number of advantages over conventional Fourier transform infrared (FTIR) spectroscopy based on incoherent sourcesJ. Mandon, G. Guelachvili, and N. Picque, Nat. Photonics 3, 99 (2009). The high spectral brightness of the comb sources allows measuring spectra with high signal-to-noise ratios in acquisition times of the order of seconds. What is more, the resolution of comb-based FTS is given by the linewidth of the comb modes rather than the optical path difference (OPD) in the spectrometer, provided that the OPD is matched to the inverse of the comb mode spacingP. Maslowski, et al., Phys. Rev. A 93, 021802 (2016); L. Rutkowski, et al., J. Quant. Spectrosc. Radiat. Transf. 204, 63 (2018). This implies that spectra with kHz resolution can be measured using OPD of the order of a few tens of cmL. Rutkowski, et al., Opt. Express 25, 21711 (2017). which is impossible in conventional FTIR spectrometers. To increase the sensitivity of direct absorption measurements, frequency combs can be efficiently coupled into enhancement cavities that increase the interaction length with the sampleM. J. Thorpe, and J. Ye, Appl. Phys. B 91, 397 (2008); A. Foltynowicz, et al., Phys. Rev. Lett. 107, 233002 (2011). In another cavity-enhanced approach, the profiles of the cavity modes are measured directly, and complex refractive index spectra of entire molecular bands are determined from the broadening and shift of the cavity modes caused by the molecular sampleA. C. Johansson, et al., Opt. Express 26, 20633 (2018). Comb-based FTS can also be combined with other detection methods, such as Faraday rotation spectroscopy to detect broadband interference-free spectra of paramagnetic moleculesA. C. Johansson, J. Westberg, G. Wysocki, and A. Foltynowicz, Appl. Phys. B 124, 79 (2018). or photoacoustic spectroscopy that allows detection in a very small sample volumeI. Sadiek, et al., Phys. Chem. Chem. Phys. 20, 27849 (2018). I will present the various implementations of comb-based FTS and show examples of high-resolution measurements of entire absorption bands in the near- and mid-infrared wavelength range.

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Footnotes:

J. Mandon, G. Guelachvili, and N. Picque, Nat. Photonics 3, 99 (2009).. P. Maslowski, et al., Phys. Rev. A 93, 021802 (2016); L. Rutkowski, et al., J. Quant. Spectrosc. Radiat. Transf. 204, 63 (2018).. L. Rutkowski, et al., Opt. Express 25, 21711 (2017)., M. J. Thorpe, and J. Ye, Appl. Phys. B 91, 397 (2008); A. Foltynowicz, et al., Phys. Rev. Lett. 107, 233002 (2011).. A. C. Johansson, et al., Opt. Express 26, 20633 (2018).. A. C. Johansson, J. Westberg, G. Wysocki, and A. Foltynowicz, Appl. Phys. B 124, 79 (2018)., I. Sadiek, et al., Phys. Chem. Chem. Phys. 20, 27849 (2018)..