The SMAUG apparatus (Spectroscopy of Molecules Accelerated in Uniform Gas flows) was developed to produce non-LTE spectra of various molecules of interest for hot astrophysical atmospheres, like the one surrounding hot Jupiters, reaching up to 2500K. High-temperature IR spectroscopic data is needed to retrieve temperature and concentration profiles from astronomical spectra. This work is done in the frame of the e-PYTHEAS project that focuses on high-temperature spectroscopy of small hydrocarbons. A small dimension Laval nozzle connected to a compact high enthalpy source equipped with cavity ringdown spectroscopy (CRDS) is used to produce vibrationally hot and rotationally cold high-resolution IR spectra of polyatomic molecules in the 1.67 μm region.^a The nozzle was designed to operate with argon heated up to 2000 K and to produce a quasi-unidirectional flow to reduce the Doppler Effect responsible for line broadening. This novel approach was applied to carbon monoxide and methane. Vibrational (T_vib) and rotational (T_rot) temperatures were extracted from the recorded infrared spectrum leading to T_vib = 1346 ± 52 K and T_rot = 12 ± 1 K for CO. A rotational temperature of 30 ± 3 K was measured for CH₄, while two vibrational temperatures were necessary to reproduce the observed intensities. The population distribution between vibrational polyads was correctly described with T_vib,I = 894 ± 47 K, while the population distribution within a given polyad (namely the dyad or the pentad) was modelled correctly by T_vib,II = 54 ± 4 K, testifying to a more rapid intra-polyad vibrational relaxation. (1,0)490
^aE.Dudás et al. J. Chem. Phys. submitted (2020)

Diffusion Monte Carlo (DMC) is a stochastic method used to generate the ground state vibrational wave function of a molecular system. Using DMC, one can understand the effects of vibrational zero-point energy on the structure of interest. Due to the informative physics in the ground state wave function, our group has previously implemented a technique to generate excited state energies and wave functions from DMC in order to understand the vibrational spectroscopy of small water-ion complexes.McCoy, A.B; Diken, E. G; Johnson, M.A. JPCA. 2009 113 (26), 7346-7352Timothy L. Guasco, T.L.; Johnson,M.A.; McCoy, A.B. JPCA. 2011 115 (23), 5847-5858 In this work, we extend this approach and apply it to larger protonated water clusters. Specifically, we are investigating the zero-order molecular vibrations and strong vibrational couplings that lead to spectral broadening. To begin, we use DMC to generate the ground state vibrational wave functions of H⁺(H₂O)_n=3,4 and D⁺(D₂O)_n=3,4. We discover tunneling in a few modes: the umbrella mode of the central hydronium, as well as the rotational coordinate of the outer water molecules. From these observations, we conclude that there are planar, high-symmetry, vibrationally-averaged structures sampled by these ions in their ground states. Using the saddle-point structures to define vibrational coordinates, we build our excited state approximation to investigate which vibrational states contribute intensity to the complicated infrared spectra. In the method’s extension, we refine our approximation of higher order excited states, and we accommodate for strong vibrational coupling through a reduced-dimensional Hamiltonian. The Hamiltonian couples states that are energetically near the fundamental excitation of the hydrogen-bonded OH stretches. The method, in general, allows us to go beyond harmonic approximations by including the anharmonicity of the ground state wave function, yet it also allows us to calculate excited state energies using simple approximations akin to the harmonic oscillator. We find the results of our calculation reinforce the previously held idea that there exist strong couplings between the hydrogen-bonded OH stretch fundamentals and a series of dark modes, which lead to intensity borrowing in both size clusters.

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McCoy, A.B; Diken, E. G; Johnson, M.A. JPCA. 2009 113 (26), 7346-7352

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Neopentane (2,2-dimethyl propane, C₅H₁₂) is an unusual hydrocarbon with tetrahedral symmetry like methane. Neopentane may be formed by organic photochemistry chemistry in the atmosphere of Titan, the largest moon of Saturn, in which 9 hydrocarbons have already been discovered, including allene that was detected very recently by high resolution infrared emission spectroscopy. High resolution infrared absorption spectra of neopentane have been recorded in the mid-infrared region at room temperature and 232 K. Neopentane is a spherical top with T_d symmetry. Four strong bands with characteristic rotational structure of t₂ modes were observed at 1257.6, 1369.4, 1472.5 and 1489.0 cm⁻¹, and a fifth very weak band was found near 924.2 cm⁻¹. Quantum chemical calculations (B3LYP/6-311++(d,p)/VPT2 and harmonic CCSD(T)-pVTZ) were carried out in both normal and local mode representations to help with the vibrational assignments: ν₁₈ (924.2 cm⁻¹), ν₁₇ (1257.6 cm⁻¹), ν₁₆ (1369.4 cm⁻¹) and the 1472.5 and 1489.0 cm⁻¹ bands are a Fermi resonance pair between the ν₁₅ fundamental and the ν₇+ν₁₉ combination mode. A rotational analysis of the two Fermi resonance bands was successful. There is also a weaker Fermi resonance interaction between the ν₁₇ fundamental and the ν₈+ν₁₈ combination mode.

Using a Fourier transform infrared spectrophotometer and a low temperature cryostat, we have obtained the IR spectra of formaldehyde dissolved in liquid krypton between 125 K and 137 K. Monomeric formaldehyde in gas phase was prepared by thermal decomposition of para-formaldehyde. Peak positions (ν), wavenumber shifts(∆ν), and full widths at half maximum (∆ν_1/2) are reported. Influence of the solvent on fundamental vibrational frequencies are studied using the polarizable continuum model (PCM). When used in combination with calculated anharmonic frequencies, the PCM model shows qualitative agreement with frequency shifts in liquid Kr. The importance of formaldehyde IR characterization around 100 K will be discussed in reference to its detection in the interstellar medium B. Zuckerman et al., Observations of Interstellar Formaldehyde, Astrophys. J., 1970, 160: 485-506. the IR detection of the ν₁ vibration in the protostar W33AE. Roueff et al., Infrared Detection of Gas Phase Formaldehyde Towards the High Mass Protostar W33A, A&A, 2006, 447: 963-969 and although the Cassini infrared spectrometer (CIRS) was not able to detect methanol, formaldehyde, and acetonitrile in Titan's atmosphere, upper limits on their abundances and formation conditions have been proposed. C.A. Nixon et al., Upper Limits for Undetected Trace Species in the Stratosphere of Titan. Faraday Discuss. 2010, 147: 65-81.^, B.N. Tran et al., Titan's Atmospheric Chemistry: Photolysis of Gas Mixtures Containing Hydrogen Cyanide and Carbon Monoxide at 185 and 254 nm, Icarus, 2008, 193: 224232

We identify a diverse class of alkaline-earth containing asymmetric top molecules, ranging from bent triatomics to molecules containing carbon rings, which can be laser cooled effectively with reasonable experimental complexity. Potential scientific impacts of these species span frontiers in controlled chemistry, quantum simulation, and searches for physics beyond the Standard Model of particle physics. We calculate vibrational branching ratios for over a dozen such molecules using a GF-matrix approach. As part of this analysis, we also describe methods to achieve rotationally closed optical cycles in these molecules. Using dispersed laser-induced fluorescence, we experimentally determine vibrational branching ratios and radiative lifetimes for the low-lying electronic states of CaSH and CaNH2, two prototypical laser-coolable asymmetric tops. Both species are found to be highly favorable for direct laser cooling. These measurements are compared to ab initio predictions. We present a practical roadmap to laser cool asymmetric top molecules, including chiral species.

Line list including line positions, intensities and broadening parameters for ¹²C³²S₂, ¹³C³²S₂, ³²S¹²C³³S and ³²S¹²C³⁴S isotopologues have been calculated using the PGOPHER program Colin M.Western. JQSRT, Vol. 186, pp.221-242 (2017). A global least-squares fit of the large set of measured line positions available in the literature to the corresponding spectroscopic parameters G_v, B_v, D_v and H_v was performed, including the most recent high-precision dual-comb laser spectroscopy measurements carried out at the University of Central Florida. A unique set of parameters for each lower and upper states were obtained. Spectroscopic constants provide energy levels for transitions. The line intensities were fit to the models derived from recent high-resolution measurements wherever possible. For the bands where no intensity measurements exist, we have used scaling factor in order to model corresponding PNNLSteven W.Sharpe, Timothy J. Johnson et al. Applied Spectroscopy, Vol.58, pp.1452-1461 (2004).ross-sections. As an example, more than 54100 ¹²C³²S₂ line positions and intensities of cold and hot bands up to J=150 have been calculated. Semi-empirical models for rotational dependence of air- and self-broadened half widths are developed based on the available experimental data. The obtained results allow improving the knowledge of spectroscopic properties of the carbon disulfide in atmospheric environmental chemistry, medical diagnostics and planetary atmospheres. In consequence of importance, this line list of CS₂ will be included in the upcoming 2020 version of the HITRAN spectroscopic database.

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Colin M.Western. JQSRT, Vol. 186, pp.221-242 (2017).. Steven W.Sharpe, Timothy J. Johnson et al. Applied Spectroscopy, Vol.58, pp.1452-1461 (2004).c

l0pt Figure Antifreeze glycoproteins play a crucial role in biochemical adaptation to supercooled waters and polar environments for the survival of many species, from animals, to plants, and insects and bacteria. Notwithstanding their vital importance for these species, and their many potential applications (medicine, biology, food industry,… ), not much is known about their principle of action, except that they prevent, somehow, the formation of ice in living systems. Accessing information on their structural and conformational properties, as well as the nature of their interaction with water, promises to shed light on the underlying mechanisms governing their function. The project focuses on connecting the conformational behaviour of these antifreezes proteins to their pivotal role in their biological activity. Natural and unnatural glycopeptides will be interrogated using IR ion-dip spectroscopic techniques, coupled with quantum chemical computation, to aid the design of ‘engineered’ antifreezes proteins, optimizing the response and facilitating the development of a new generation of this type of proteins.I. A. Bermejo, I. Usabiaga, I. Compañón, J. Castro-López, A. Insausti, J. A. Fernández, A. Avenoza, J. H. Busto, J. Jiménez-Barbero, J. L. Asensio, J. M. Peregrina, G. Jiménez-Osés, R. Hurtado-Guerrero, E. J. Cocinero, F. Corzana, J. Am. Chem. Soc., 2018, 140, 31, 9952-9960.html:<hr /><h3>Footnotes: I. A. Bermejo, I. Usabiaga, I. Compañón, J. Castro-López, A. Insausti, J. A. Fernández, A. Avenoza, J. H. Busto, J. Jiménez-Barbero, J. L. Asensio, J. M. Peregrina, G. Jiménez-Osés, R. Hurtado-Guerrero, E. J. Cocinero, F. Corzana, J. Am. Chem. Soc., 2018, 140, 31, 9952-9960.

High Resolution infrared spectra of six isotopomers of bromomethane (CH₃Br, CD₃Br, ¹³CH₃Br – with the ⁷⁹Br and ⁸¹Br isotopes for each isotopomer) have been recorded at the Pacific Northwest National Laboratory. Here, we will present an analysis of fundamental, overtone and combination vibrational states for CH₃Br below 1811 cm⁻¹. Previous high-resolution work in this region for bromomethane focused mainly on obtaining frequency positions and line strengths for atmospheric sensing purposes. However, our work on this molecule focuses on obtaining precise rovibrational parameters that will serve as a foundation for the analysis of higher energy combination and overtone bands involving these states. These precise measurements facilitate the identification of subtle rotational and vibrational interactions that have been theoretically predicted, but have never before been characterized. Specifically, the Fermi resonance between ν₅ (E) and ν₃+ν₆ (E) is identified as well as a weak Coriolis interaction between ν₂ (A₁) and ν₃+ν₆ (E). The 3ν₃ vibrational state has been analyzed for the first time, and hyperfine splittings similar to those found in CH₃I for low K, J levels have also been observed.

Molecules that contain radium are promising candidates as probes of physics beyond the Standard Model. The large nuclear octupole deformation of the radium atom and large effective electric fields found within molecules could lead to extremely sensitive tests of fundamental symmetries. However, there exist little to no spectroscopic data on molecules of interest. In order to explore the electronic and vibrational states of these molecules we have developed a system to do a broad spectrum search with laser ablation molecular spectroscopy (LAMS). Targets containing the constituent atoms are ablated with a pulsed laser and light is collected from the resulting plasma plume where molecules are formed. The fluorescence is then analyzed looking for the new molecular transitions. Barium is used as a surrogate as a means to test target production and the sensitivity of the method to unknown molecular transitions from a small amount of material. The development of the experiment and progress towards the detection of novel barium molecules will be presented. This work is supported by the U.S. DOE, Office of Science, Office of Nuclear Physics, under contract DE-AC02-06CH11357.

Complexes of Co⁺(H₂O) and Co⁺(D₂O) are produced via laser vaporization of cobalt metal in a supersonic expansion of rare gas seeded with water. Infrared photodissociation spectroscopy is accomplished with the aid of rare gas tagging by He, Ne, or Ar. The effect of Co+ on the ortho-para nuclear spin statistics of H₂O and D₂O are investigated. The OH stretching frequencies of water were found to red shift by about 40 cm⁻¹, and the water bending mode was found to blue shift by 23 cm⁻¹. Rotational resolution was achieved for helium tagged water complex. The combined effect of spin-orbit coupling and spin-rotation coupling in these complexes is discussed and compared to the previously studied systems Sc⁺(H₂O) and Ti⁺(H₂O). Electronic structure calculations with CASSCF/cc-pVTZ were used to determine the single reference character of the ground electronic state. MN15/cc-pVTZ was used to compute vibrational frequencies.

Density functional theory is a common tool for calculating infrared (IR) spectra. While harmonic approximation usually performs well on the molecules of small to medium size, it fails for predicting IR spectra of large ions. On the other hand, classical anharmonic treatment such as VPT2 or VSCF, becomes prohibitively expensive for large molecules. An alternative approach is to calculate the IR spectrum by the Fourier transform of the dipole moment autocorrelation function from a classical trajectory,[1] e.g., from Born-Oppenheimer molecular dynamics (BOMD). In contrast to the harmonic approximation, BOMD includes the vibrational couplings as well as conformational sampling at a given temperature. In the Chen group, we have recently started studying IR spectra of large ions in the gas phase.[2] In order to understand the complicated IR fingerprints of those systems, we investigated the possibility of calculating IR spectra by BOMD simulations with the semi-empirical GFN-xTB methods,[3,4] and used this approach in combination with DFT to understand experimental IR spectra. References: [1] D.W. Noid, M.L. Koszykowski, and R.A. Marcus, The Journal of Chemical Physics 67, 404 (1977). [2] A. Tsybizova, L. Fritsche, V. Gorbachev, L. Miloglyadova, and P. Chen, J. Chem. Phys. 151, 234304 (2019). [3] S. Grimme, C. Bannwarth, and P. Shushkov, J. Chem. Theory Comput. 13, 1989 (2017). [4] C. Bannwarth, S. Ehlert, and S. Grimme, J. Chem. Theory Comput. 15, 1652 (2019).