For more than half a century, gas-phase reaction networks of rapid ion-molecule and neutral-neutral reactions have played a fundamental role in aiding our understanding of the evolution of the interstellar medium (ISM). However, with about 200 molecules detected in interstellar and circumstellar environments, these models fail to explain the synthesis of ubiquitous complex organic molecules (COMs) – organics containing several atoms of carbon, hydrogen, nitrogen, and oxygen – predicting abundances which are lower by several orders of magnitude compared to observations toward hot molecular cores like Sagittarius B₂(N). Here, we report that key COMs - methanimine (CH₂NH) and ethylenediamine (NH₂CH₂CH₂NH₂) along with n-methylformamide (CH₃NHC(O)H) can be synthesized within interstellar ices containing methylamine (CH₃NH₂) at temperatures as low as 5 K via an facile non-equilibrium chemistry initiated by energetic electrons initiated by galactic cosmic rays once penetrating interstellar ices. After the radiation exposure, the subliming molecules were analyzed isomer selectively after single photon vacuum ultraviolet ionization coupled with a reflectron time-of-flight mass spectrometer (PI-ReTOF-MS). This methodology has several advantages compared to traditional infrared spectroscopy of ices such as the possibility to identify structural isomers of complex organics. The underlying reaction mechanisms leading to methanimine, ethylenediamine, and n-methylformamide in methylamine bearing ices are compared to the chemistry of isoelectronic methanol ices studies previously in our laboratory, revealing exciting similarities, but also differences in the synthesis of complex organic molecules in the interstellar medium. We thank the US National Science Foundation (AST-1505502) for support to conduct the experiments and data analysis. Furthermore, we thank the W. M. Keck Foundation for financing the experimental setup.

We present the current status of an experimental setup in which astronomical receivers and spectrometers are coupled to a reaction chamber to study the spectroscopy and chemical evolution of gas mixtures via their rotational emission lines. In a first proof of concept a small prototype reactor was placed in the beam path of the Aries 40 m radio telescope (Yebes, Guadalajara, Spain) facing the Q-band receiver operating in the 41-49 GHz frequency range providing 2 GHz bandwidth and 38 kHz resolution. Experiments with static samples or in flow mode, exposed to UV irradiation or an inductively coupled cold plasma were performed and the feasibility of the experiment demonstratedI. Tanarro et al. Astron. & Astrophys. 609, A15 (2018) In a second phase, new receivers have been designed and built by the team of astronomers and engineers at the Yebes observatory, and are now coupled to a new larger reaction chamber in a dedicated laboratory. The new receivers cover the 31.5-50 GHz and 72-116 GHz bands quasi-simultaneously, with resolution  ∼ 38 kHz. The performance and first results of the system will be discussed.

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Footnotes:

I. Tanarro et al. Astron. & Astrophys. 609, A15 (2018).

O(¹D) insertion reactions with stable precursors have proved an efficient way of producing important prebiotic molecules that are highly reactive and otherwise unstable under laboratory conditions. In 2015, Hays et al.B. M.Hays, N. Wehres, B. Alligood DePrince, A. A.M. Roy, J. C. Laas, S. L. Widicus Weaver, Chem.Phys. Lett., 630, 18 (2015)eported successful production of gaseous methanol and vinyl alcohol by exothermic O(¹D) insertion into methane and ethylene, respectively, and collected their rotational spectra in the millimeter/submillimeter region. Prior to this, in 2013 Hays et al.B. M. Hays, S. L. Widicus Weaver, J. Phys. Chem., 117, 7142 (2013)eported a computational study predicting the formation of methanediol, methoxymethanol and aminomethanol, through O(¹D) insertion into methanol, dimethyl ether and methylamine, respectively. These species are all important prebiotic molecules and have been shown to be stable under interstellar conditions. We therefore seek to collect their spectra for comparison to interstellar observations. Here we will report experimental progress toward producing and characterizing the spectra of aminomethanol and methanediol using O(¹D) insertion reactions and millimeter/submillimeter spectroscopy.

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Footnotes:

B. M.Hays, N. Wehres, B. Alligood DePrince, A. A.M. Roy, J. C. Laas, S. L. Widicus Weaver, Chem.Phys. Lett., 630, 18 (2015)r B. M. Hays, S. L. Widicus Weaver, J. Phys. Chem., 117, 7142 (2013)r

The physiochemical impact of cosmic rays on interstellar regions is widely known to be significant Indriolo, N. & McCall, B. J.,Chem. Soc. Rev., 42, 7763-7773, 2013 Indeed, the cosmic ray-driven formation of H₃⁺ via the ionization of H₂ was shown to be of key importance in even the first astrochemical models Herbst, E. & Klemperer, W., Ap.J., 185, 505-534, 1973 Later, cosmic rays were implicated in the collisional excitation of H₂, which leads to the production of internally produced UV photons that also have profound effects on the chemistry of molecular clouds Prasad, S. S. & Tarafdar, S. P.,Ap.J., 267, 603-609, 1983 Despite these key findings, though, attempts at a more complete consideration of interstellar radiation chemistry have been stymied by the lack of a general method suitable for use in astrochemical models and capable of preserving the salient macroscopic phenomena that emerge from a large number of discrete microscopic events. Recently, we have developed a theoretical framework which meets these criteria and allows for the estimation of the decomposition pathways, yields, and rate coefficients of radiation-chemical reactions Shingledecker, C. N. & Herbst, E., Phys. Chem. Chem. Phys., 20, 5359-5367, 2018 In this talk, we present preliminary results illustrating the effect of solid-phase radiation chemistry on models of TMC-1 in which we consider the radiolysis of the primary ice-mantle constituents of dust grains. We further discuss how the inclusion of this non-thermal chemistry can lead to the formation of complex organic molecules from simpler ice-mantle constituents, even under cold core conditions. Indriolo, N. & McCall, B. J.,Chem. Soc. Rev., 42, 7763-7773, 2013. Herbst, E. & Klemperer, W., Ap.J., 185, 505-534, 1973. Prasad, S. S. & Tarafdar, S. P.,Ap.J., 267, 603-609, 1983. Shingledecker, C. N. & Herbst, E., Phys. Chem. Chem. Phys., 20, 5359-5367, 2018.

Studying the chemical evolution of the interstellar medium (ISM) is critical for understanding chemical processes which take place during the formation of stars and planetary systems. The gas-phase composition of interstellar space is revealed through remote observations employing high-resolution spectroscopy. It is believed that many complex organics found in the ISM, some of which are of prebiotic interest, first formed in the ices coating interstellar dust grains. The results of laboratory simulations of interstellar ices provide great insight into how complex organics form and/or evolve in the ISM. Previous experimental techniques have monitored the thermal and photoprocessing of relevant ices via infrared spectroscopy while studying the sublimated gases with mass spectrometry. Here we will discuss a new approach that uses noninvasive submillimeter spectroscopy to analyze the gas-phase reactions occurring above the ice during processing. New results and experimental improvements will be discussed.

The ammonium-d cation (NDH₃⁺) is the singly-deuterated isotologue of ammonium (NH₄⁺), an abundant species in terrestrial chemistry that has been proposed as a key species in the chemistry of interstellar objects. Unlike NH₄⁺, NDH₃⁺ has a nonzero rotational dipole transition moment, so it can be detected by its microwave emissions. To assist in the detection of this ion, we have collected rovibrationally resolved infrared spectra of its symmetric (ν₁, A₁) and asymmetric (ν₄, E) N–H stretching modes, with special attention to accurately determining its ground-state rotational constants. In this study, NDH₃⁺ is generated by seeding NDH₂ in a H₂/Ne/He mixture through a pulsed slit discharge. Electron ionization of H₂ in the mixture produces H⁺, which readily protonates other H₂ molecules to form H₃⁺; this H₃⁺ goes on to protonate NDH₂. The resulting NDH₃⁺ ions are cooled in a slit jet supersonic expansion to a rotational temperature of 40 K. Rotational constants for the ground state and both singly-excited vibrational states, as well as the ν₁ and ν₄ band origins, are obtained by least-squares fitting of the sub-Doppler rotational structure to a symmetric top Hamiltonian. The fitted band origins agree with the best theoretical predictions to within 1 cm⁻¹.

OH⁺ is an important astrophysical species. OH+ has been detected in the interstellar medium by UV and terahertz spectroscopy. Following the recent analysis of OH⁺ emission spectra,Hodges, J. N., & Bernath, P. F. Astrophys. J., 840.2 (2017) 81mpirical potential energy surfaces have been calculated for the A³Π and X³Σ⁻ states using the RKR method. Ab initio transition and dipole moment functions were calculated and together with the potential energy surfaces have been used to compute oscillator strengths using Le Roy’s LEVEL program.Le Roy, R. J., J. Quant. Spectrosc. Radiat. Transf. 186 (2017) 167he new oscillator strengths account for the Herman–Wallis effect, a rotational dependence in the vibrational wavefunction, and are now in good agreement with the measured lifetime.Möhlmann, G. R., et al., Chem. Phys. 31.2 (1978) 273he Herman–Wallis effect creates a 5% difference in UV oscillator strengths by J" = 15 and an 80% difference in oscillator strengths by J" = 10 in the IR. We recommend these new oscillator strengths be used to determine OH⁺ column densities.

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Footnotes:

Hodges, J. N., & Bernath, P. F. Astrophys. J., 840.2 (2017) 81e Le Roy, R. J., J. Quant. Spectrosc. Radiat. Transf. 186 (2017) 167T Möhlmann, G. R., et al., Chem. Phys. 31.2 (1978) 273T

Absorption cross sections for a range of small hydrocarbons, from C2-C4, in the far and mid IR spectral regions are presented. Cross sections were obtained from high resolution spectra recorded at cold temperatures from experiments performed at two synchrotron facilities: the Australian Synchrotron (AS) and the Canadian Light Source (CLS), as well as at Old Dominion University (ODU). The experimental conditions that were sampled (pressure, composition and temperature) were chosen to mimic those found in the planetary atmospheres of Titan, Saturn and Jupiter. These cross sections can be used to determine molecular abundances from remote sensing observations.

Interstellar dust is an integral part of the interstellar medium and is important for star forming processes and the associated chemical evolution in these regions. However the formation of dust is still not well understood. Around oxygen rich late type stars, titanium oxides are thought of being an important seed molecule of the dust formation and has been observed at optical and radio wavelengths.

A new generation of high resolution infrared telescope instruments, like TEXES at Gemini North or EXES onboard SOFIA, allows the identification of astrophysical molecules by means of their rovibrational spectra, probing warm atmospheres of evolved late type stars in the mid-infrared.

In this talk we present high resolution laboratory spectra of titanium monoxide (TiO) and its isotopologues in the gas-phase around 1000cm⁻¹(10 μm). In a global fit we determine molecular parameters of the vibrational excited states with high accuracy. In our experiments, molecules are produced using high intense laser pulses to ablate a titanium sample in an atmosphere of nitrous oxide diluted in helium buffer gas. Guided through a reaction channel different molecules - including TiO - are formed. Subsequent adiabatic expansion in a supersonic jet cools down the molecules to rotational temperatures of around 30 K. To record a rotationally resolved infrared spectrum a quantum cascade laser is used.

The relative abundance of HCN/HNC is a ubiquitous issue in astrochemistry. This ratio is largely governed by competition between thermodynamic stability and kinetics: in cold dense clouds, the thermodynamically unfavorable HNC is enhanced, while in hot cores and young stellar objects there is a much stronger preference for HCN. Efforts to develop a consistent and universally accepted set of reaction rates and thermochemical parameters involving both gas- and condensed-phase dynamics has proven challenging. Considerable interest has focused on accurate determinations of molecular properties, and many theoretical and experimental efforts, spanning several decades, have sought to provide the necessary rates and enthalpies. Despite much work, estimates of the uncertainty of enthalpies and rates vary substantially, particularly with respect to quantum chemical treatments that involve a plethora of basis sets and methods. To address this issue, we have undertaken a systematic study to calculate a consistent set of thermochemical quantities and rates involving gas-phase reactions presumed to be important in determining the branching between HCN and HNC in astrophysical environments. Using the HEAT345(Q) method, we have calculated the energetics of neutral and ion reactants and products. This method routinely achieves chemical accuracy ( 1 kJ/mol/120 K) without empirical corrections. We validate our thermochemical network by comparison with reliable databases such as the ATcT, and by doing so lends confidence into the species that are not yet included in databases. Finally, we report reaction rates for significant reactions from first principles (V)TST theory.

The Unidentified Infrared Bands are now widely believed to originate from the emission of large, aromatic molecules in high-energy environments. Despite this, no individual species has been identified as a carrier, and indeed the only five- or six-membered aromatic ring molecule reported in the ISM is benzene, which is seen in only a small handful of sources at infrared wavelengths. Here, I will discuss a dedicated laboratory, observational (GBT), and modeling effort which has resulted in the first definitive radio identification and quantification of a benzene-ring containing aromatic molecule: benzonitrile (c-C₆H₅CN). The results will shed light on the probable formation pathways for larger aromatic species, and have identified a successful methodology for future, comprehensive investigations.

Benzonitrile (c-C₆H₅CN) has recently been detected in the interstellar medium - the first molecule containing a benzene ring to be observed by radio astronomy. Its detection in a cold, starless dark cloud affords one the opportunity to probe aromatic chemistry at the earliest stages of the star formation process. Here, we explore the formation chemistry of benzonitrile using a combination of laboratory microwave spectroscopic and quantum chemical approaches. We demonstrate the synthesis of benzonitrile from a variety simple, acyclic precursors (acetylene [HCCH], diacetylene [HC₄H], cyanoacetylene [HC₃N], and 1,3-butadiene [CH₂(CH)₂CH₂]), providing definitive evidence for facile bottom-up generation of aromatic carbon chemistry from small interstellar precursors. The results show that benzonitrile can already be used as a reliable proxy for the presence of benzene in the ISM, and that there may exist a much larger array of aromatic species that are `hidden' just below the current sensitivity of spectral surveys.