Small reactive organic molecules are key intermediates in interstellar chemistry, leading to the formation of biologically-relevant species as stars and planets form. These molecules are identified in space via their pure rotational spectral fingerprints in the far-IR or terahertz (THz) regime. Despite their fundamental roles in the formation of life, many of these molecules have not been spectroscopically characterized in the laboratory, and therefore cannot be studied via observational astronomy. The reason for this lack of fundamental laboratory information is the challenge of spectroscopy in the THz regime combined with the challenge of studying unstable molecules. Our laboratory research involves characterization of astrophysically-relevant unstable species, including small radicals that are the products of photolysis reactions, organic ions formed via plasma discharges, and small reactive organics that form via O(¹D) insertion reactions. Our observational astronomy research seeks to examine the chemical mechanisms at play in a range of interstellar environments and to identify chemical tracers that can be used as clocks for the star-formation process. In this talk, I will present recent results from our laboratory and observational studies that examine prebiotic chemistry in the interstellar medium. I will discuss these results in the broader context of my integrative research program that encompasses laboratory spectroscopy, observational astronomy, and astrochemical modeling.

The chemical and structural diversity and the extent of post-transcriptional modification of RNA are remarkable! Currently there are more than 163 naturally-occurring modified nucleosides known. Modified nucleosides have also been a target for pharmaceutical application as potential anticancer and antiviral agents such that many more synthetically-modified nucleosides have been studied. While the biochemical and physiological roles of modified nucleosides have been elucidated in some cases, their importance to RNA biochemistry is still largely unknown and underappreciated. Thus, comparative studies of the canonical versus naturally-occurring and synthetically-modified nucleosides to elucidate changes in structure and glycosidic bond stability arising from modifications are important to understanding their mechanisms of action. Synergistic tandem mass spectrometry and computational chemistry approaches are used to characterize the structures and relative glycosidic bond stabilities of the protonated and sodium cationized forms of the canonical DNA and RNA nucleosides and a wide variety of naturally-occurring and synthetic nucleosides. Vibrational frequency-resolved infrared multiple dissociation (IRMPD) action spectroscopy experiments coupled with spectral analyses of the stable low-energy conformers and their predicted linear IR spectra are used to elucidate the gas-phase conformations of these nucleosides. The stable structures of the nucleosides, their relative stabilities, and predicted linear IR spectra are determined using ab initio and density functional theory methods. Energy-resolved collision-induced dissociation (ER-CID) experiments coupled with survival yield analyses are used to elucidate the relative glycosidic bond stabilities of the nucleosides. Differences in structure induced by modifications and trends in the relative glycosidic bond stabilities of the canonical versus modified nucleosides are examined in detail. Implications of nucleoside modifications on structure-function relationships are discussed.

Irradiation of ultrashort laser pulses onto a molecular ensemble inherently results in the creation of a quantum wave packet (WP), i.e., a coherent superposition of several (or sometimes many) eigenstates. It is an ultimate goal in modern molecular physics to establish the way for creating WPs as designed, and it is also essential for advanced WP manipulation to know how to characterize the WP experimentally. Over the last two decades, intense nonresonant excitation has been extensively adopted to realize “nonadiabatic molecular alignment” or “nonadiabatic rotational excitation,” where the impulsive torque due to anisotropic molecular polarizability instantaneously align the molecules and their rotation is coherently excited in the vibronic ground-state manifold.Y. Ohshima and Hasegawa, Int. Rev. Chem. Phys. 29, 619 (2010).volution of the rotational WP thus created can be tracked as a series of images for the time-dependent molecular orientational distribution, e.g., by implementing pump-probe Coulomb explosion ion-imaging measurements. We will represent some examples of such “molecular movies” taken with a newly configured imaging configuration,K. Mizuse, R. Fujimoto, and Y. Ohshima, Rev. Sci. Instrum. 90, 103107 (2019).hich is capable to clearly capture the time-dependent nodal structures, instantaneous alignment, angular dispersion, and fractional revivals of the rotational WP while the molecular ensemble keeps rotating in one direction.K. Mizuse, K. Kitano, H. Hasegawa, and Y. Ohshima, Sci. Adv. 1, e1400185 (2015).ave-packet imaging will also be developed as a new approach in molecular spectroscopy, since energy intervals between the eigenstates that constitute the WP are encoded in the molecular movies shoot by the method. We will show some recent results along this direction; rotational spectra have been successfully extracted for homodimers of nonpolar molecules, which have been scarcely investigated because of the difficulty in recording or analyzing their IR or microwave spectrum.

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Footnotes:

Y. Ohshima and Hasegawa, Int. Rev. Chem. Phys. 29, 619 (2010).E K. Mizuse, R. Fujimoto, and Y. Ohshima, Rev. Sci. Instrum. 90, 103107 (2019).w K. Mizuse, K. Kitano, H. Hasegawa, and Y. Ohshima, Sci. Adv. 1, e1400185 (2015).W

The study of weakly bound complexes has been a multidimensional endeavor for over forty years. In this talk, we focus on microwave spectroscopic studies of reactive complexes, i.e., those formed from molecules that would ordinarily react under bulk conditions but may or may not yield products in an isolated cluster. Three types of systems will be discussed. First, we present a brief review of partially bound Lewis acid-base complexes and describe the role of crystallization in driving chemical bond formation. With that as an historical backdrop, we then describe the recent discovery of carboxylic sulfuric anhydrides. These species are shown to form via a nearly barrierless cycloaddition reaction between SO₃ and carboxylic acids within a putative SO₃-RCOOH complex. Results of statistical thermodynamic calculations are presented and the potential atmospheric significance of these species will be discussed. Finally, we consider the role of microsolvation in promoting the spontaneous ionization of protic acids in their complexes with water. New work on the mono-, di-, and trihydrates of triflic acid demonstrates that only three water molecules are needed before the system is best regarded as a partially solvated hydronium triflate ion pair.