Gas-phase cyclobutyl radical (·C₄H₇) is generated at a rotational temperature of 15 K in a slit-jet discharge mixture of 70% Ne/30% He and 0.5-0.6% cyclobutyl bromide (C₄H₇Br). The fully rovibrationally resolved absorption spectra of the α-CH stretch fundamental band are observed and analyzed, yielding the first precision structural information for this radical species. The band origin is determined to be 3068.7801(25) cm⁻¹, which from previous infrared spectroscopic studies of cyclobutyl radicals in dropletsA. R. Brown, P. R. Franke and G. E. Douberly, "Helium nanodroplet isolation of the cyclobutyl, 1-methylallyl, and allylcarbinyl radicals: Infrared spectroscopy and ab initio computations," J. Phys. Chem. A 121, 7576-7587 (2017).mplies a 0.8 cm⁻¹ blue shift due to the presence of liquid helium. This value is also in good agreement with high-level ab initio calculations at CCSD(T) level of theory with a PVnZ (n = 2,3) and ANOn (n = 0,1) basis set, which predicts an anharmonic frequency of 3076.4 cm⁻¹ from second-order vibrational perturbation theory (VPT2).D. A. Matthews, L. Cheng, M. E. Harding, F. Lipparini, S. Stopkowicz, T.-C. Jagau, P. G. Szalay, J. Gauss and J. F. Stanton, "Coupled-cluster techniques for computational chemistry: The CFOUR program package," J. Chem. Phys. 152, 214108 (2020). complete rovibrational analysis is underway, progress toward which will be reported. Of particular dynamical interest in such results will be the large amplitude nature of the ring puckering motion, specifically whether this radical possesses a planar (C_2v) or puckered (C_s) geometry. While CCSD(T) theoretical calculations predict a C_s electronic minimum and a C_2v first-order saddle point, the ratio of out-of-plane puckering frequency to interconversion barrier constitutes the dominant influence on the vibrationally averaged molecular geometry and dynamics of large amplitude motion for cyclobutyl radical.

---

Footnotes:

A. R. Brown, P. R. Franke and G. E. Douberly, "Helium nanodroplet isolation of the cyclobutyl, 1-methylallyl, and allylcarbinyl radicals: Infrared spectroscopy and ab initio computations," J. Phys. Chem. A 121, 7576-7587 (2017).i D. A. Matthews, L. Cheng, M. E. Harding, F. Lipparini, S. Stopkowicz, T.-C. Jagau, P. G. Szalay, J. Gauss and J. F. Stanton, "Coupled-cluster techniques for computational chemistry: The CFOUR program package," J. Chem. Phys. 152, 214108 (2020).A

Current astronomical observations, for instance with ALMA and NOEMA, extend well into the submillimeter-wave frequency domain. For many molecules, including some that have already been detected in the interstellar medium, laboratory data remain limited to the microwave and millimeter-wave regions. This is particularly striking for numerous reactive species difficult to produce in the laboratory. Considering that frequency extrapolation in absence of laboratory data is particularly unreliable, this lack of measurements surely prevents a thorough analysis of the observational data at high frequencies. The CH₃O radical is one such species: it is a known interstellar molecule [1] for which laboratory measurements do not extend beyond 370 GHz [2]. In this work, we have investigated the pure rotational spectrum of CH₃O toward the terahertz domain. The radical was produced by H-abstraction from methanol using atomic fluorine, itself produced using a microwave discharge in F₂ diluted in He, a method that we successfully used recently to investigate the rotation-tunneling spectrum of the CH₂OH radical [3]. Compared to that previous work, several enhancements have been made to our (sub)millimeter-wave spectrometer that now allows for double-pass into the absorption cell and magnetic-field modulation. The strength of the double-modulation (source frequency and magnetic field) scheme is that only transitions of open-shell species are visible over a completely flat baseline, a feature that has proven invaluable in the case of CH₃O to disentangle an otherwise dense spectrum with numerous strong transitions arising from the precursor or other reaction products (such as H₂CO). Overall, about 500 lines of CH₃O have been recorded up to 900 GHz, with accuracies ranging from 10 to 200 kHz. These transitions have been fit, together with available pure rotation literature data, to a rigid-rotor Hamiltonian using the SPFIT/SPCAT software.

The pure rotational spectrum of the open shell difluorocyanomethyl radical, · CF₂CN, has been measured using two Balle-Flygare-type cavity Fourier-Transform-Microwave (FTMW) spectrometers both equipped with pulsed discharged r0pt Figure nozzles. A total of 156 transitions (from N = 1 – 0 to 6 – 5, and K_a = 0, 1, 2, 3) in the electronic ground state were observed between 6.5 GHz and 38.4 GHz with a typical linewidth of approximately 5 kHz full-width-half-maximum. A Hamiltonian that included semi-rigid rotor, spin-rotation, and nuclear hyperfine parameters was fit to the observed data set and these parameters have been interpreted and compared to similar radicals. Excellent agreement between experimental and uB3LYP/aug-cc-pVQZ calculated rotational constants, the experimental inertial defect, -0.6858(2) uŲ, and the failure of a coupling scheme in which the fluorine nuclei are treated as identical and related by a C_2v symmetry axis combine to indicate a nonplanar structure for the · CF₂CN radical.

A new program, written in Julia, has been written to simulate and fit spectra of radicals with 3-fold internal rotors. The program now uses a single diagonalization stage implementation of the Rho Axis Method to provide more direct usage of the wavefunction symmetries for the A states. The three different methyl positions provided test cases of potential spin-torsion coupling with varying internal barrier heights of about V₃ ≈ 206 cm⁻¹in ortho, V₃ ≈ 64 cm⁻¹in meta, and V₆ ≈ 7 cm⁻¹in para. Spectroscopic parameters determined from CCSD(T)/ANO0 calculations provided test cases for assigning states and simulating the spectra. The rotational spectra of ortho-, meta-, and para-methyl-phenoxyl radicals was collected through Chirped-Pulse Fourier Transform Microwave Spectroscopy. The radicals were produced from the appropriate methyl anisole precursors through pyrolysis in a SiC pyrolysis source attached to a pulsed valve. The temperature of the reactor was monitored with an infrared camera and the production of the radicals was monitored with 118 nm photoionization -Time of Flight Mass Spectrometry. Once the optimal temperature of the pyrolysis source was determined, the rotational spectrum was recorded from 7.5 - 17.5 GHz. Each radical was fit as a closed-shell species using RAM36 and as an open-shell species using the new program which also included spin-torsion coupling terms.

Studying the different possible reactions and their dynamics under the low-temperature conditions of the interstellar medium and various planetary atmospheres is essential to understand the chemical evolution of various species detected in these environments. I will discuss the CPUF (Chirped Pulse in Uniform supersonic Flow) technique, which is a combination of the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Supersonic Uniform Flow) method to provide a low temperature environment and chirped-pulse Fourier transform millimeter spectroscopic detection. This technique has been further modified with an additional expansion chamber to enhance the detection of a wider variety of species and to overcome pressure effects in a CRESU flow. I will show our measurements for the reaction of CN radical with propene down at 35 K. I will discuss the impact of these experimental measurements, their application to astrochemical studies, and the future outlook for this technique at Rennes.

Studying the chemical inventory of the interstellar medium (ISM) is critical to developing new theories of molecular formation and evolution. Furthermore, the search for biologically-relevant species and their precursors has been at the forefront of astrobiology and astrochemistry in recent years. As such, this work focuses on the dissociation products of methylamine (CH₃NH₂), a known precursor to the simplest amino acid, glycine (C₂H₅NO₂). It is likely that the radical products of cosmic-ray induced photodissociation of methylamine are important in prebiotic interstellar pathways as well as atmospheric models of planetary bodies such as Titan. Therefore, we are studying the radical species produced in a methylamine discharge as a guide for future studies of methylamine photodissociation. Our initial molecular target is the CH₂NH₂ radical, for which no rotational spectroscopic information is available. We examined the structure of this radical using high-level computational methods and then predicted the rotational spectrum based off of this information. We then compared these predictions to the rotational spectra of species obtained using a high voltage discharge of methylamine in argon at the throat of a supersonic expansion. Here we will present the spectroscopic predictions and the initial experimental results for CH₂NH₂, and discuss the implications of this work for astrochemistry and astrobiology.

Methylamine (CH₃NH₂) is considered to be a potential precursor for the formation of interstellar glycine through the reaction between aminomethyl radical (•CH₂NH₂) and HOCO, but direct evidence of the formation and spectral identification of •CH₂NH₂ remains unreported. Taking advantage of unique properties associated with the para-hydrogen (p-H₂) matrix, we performed the reaction H + CH₃NH₂ in solid p-H₂ at 3.2 K. To generate H atoms, photolysis at 365 nm of a co-deposited mixture of CH₃NH₂/p-H₂ and Cl₂ to produce Cl atoms and subsequent IR irradiation for promoting the Cl + H₂ (ν = 1) → H + HCl reaction were carried out. IR spectra of •CH₂NH₂ and CH₂NH were observed upon UV/IR irradiation and when the matrix was maintained in darkness. The new IR spectrum of •CH₂NH₂ clearly indicates that •CH₂NH₂ can be formed from the reaction H + CH₃NH₂ in dark interstellar clouds. Experiments on CD₃NH₂ produced CHD₂NH₂, in addition to •CD₂NH₂ and CD₂NH, confirming the occurrence of H addition to •CD₂NH₂. The potential-energy scheme of H + CH₃NH₂ reactions reveals the feasibility of sequential H-abstraction and H-addition reactions for the formation of products observed in this study. The observed dual-cycle mechanism containing two consecutive H-abstraction and two H-addition steps chemically connects CH₃NH₂ and CH₂NH and might imply their quasi-equilibrium. In another experimental method, photolysis at 250 nm of a H₂O₂-doped CH₃NH₂/p-H₂ matrix was performed to generate •OH to facilitate the •OH + CH₃NH₂ reaction; further reaction of •OH + H₂ → H₂O + H might also trigger the H + CH₃NH₂ reaction. Significantly more •CH₂NH₂ was produced than in CH₃NH₂/Cl₂/p-H₂ experiments, consistent with a barrier predicted for •OH + CH₃NH₂ much smaller than that for H + CH₃NH₂. All species observed herein are plausible starting materials for interstellar glycine in molecular clouds.

High-resolution EPR spectra of CH₃ radicals in the solid CH₄ and CD₄ matrices were obtained and analyzed. The change in the symmetry of a small impurity molecule freely embedded in the matrix crystal lattice in comparison with the symmetry of this molecule in the gas phase, which we found on the example of the CH₃ radical in the CH₄ and CD₄ solids, is expected to be a fairly general and important effect for spectroscopy. The data we obtained on the orientation mobility of methyl radical in the methane matrices in comparison with the results for other matrices indicate a sufficiently rapid sub-barrier reorientation of the methyl radical and the correlated tunneling reorientation of the methane molecules, which occurs even at helium temperatures in an orientationally ordered solid.

Methacrolein oxide (MACRO, CH₂C(CH₃)CHOO) is an important Criegee intermediate produced in ozonolysis of isoprene, the most abundantly-emitted non-methane hydrocarbon in the atmosphere. We employed a step-scan Fourier-transform infrared spectrometer to investigate the source reaction of MACRO in laboratories. Upon UV irradiation of precursor 1,3-diiodo-2-methyl-prop-1-ene CH₂IC(CH₃)CHI (1), the 3-iodo-2-methyl-prop-1-en-3-yl CH₂C(CH₃)CHI radical (2) was detected, confirming the fission of the allylic C-I bond rather than the vinylic C-I bond. Upon UV irradiation of (1) and O₂ near 21 Torr, anti-trans-MACRO (3a) was observed to have an intense OO-stretching band near 917 cm⁻¹, much greater than those of syn-CH₃CHOO and (CH₃)₂COO, supporting a stronger O-O bond in MACRO because of resonance stabilization. At increased pressure (86-346 Torr), both reaction adducts CH₂C(CH₃)CHIOO (4) and (CHI)C(CH₃)CH₂OO (5) radicals were observed, indicating that O₂ can add to either carbon of the delocalized propenyl radical moiety of (2). We also employed a quantum-cascade laser and an UV laser to investigate the yield and kinetics of MACRO. The yield of MACRO is only  5 % from the source reaction, significantly smaller than other carbonyl oxides. The rate coefficients of the formation reaction and the self-reaction of MACRO will also be discussed.

The reaction of Criegee intermediates with HNO₃ have been thought to be important in the oxidation of atmospheric HNO₃ because of the fast reaction rates, over 3 orders of magnitude larger than that of the OH + HNO₃ reaction.Khan, M. A. H.; Percival, C. J.; Caravan, R. L.; Taatjes, C. A.; Shallcross, D. E. Environ. Sci.: Processes Impacts 2018, 20, 437–453.n particular, a new catalytic conversion of the simplest Criegee intermediate CH₂OO to OH and HCO radicals by HNO₃ was proposed in recent theoretical study.Raghunath, P.; Lee, Y.-P.; Lin, M. C. J. Phys. Chem. A 2017, 121, 3871– 3878.erein, the mid-infrared dual-comb spectrometersLuo, P.-L.; Horng, E.-C. Commun Chem 2020, 3, 95; Luo, P.-L. Opt. Lett. 2020, 45, 6791–6794.ith the capability of widely wavelength tunability and switchable dual-comb and continuous-wave operation modes were employed to investigate the reaction kinetics and determine the branching ratios of the primary product channels in the reaction CH₂OO + HNO₃. Based on quantitative determinations of CH₂OO, CH₂O, OH and HO₂ radicals under various experimental conditions, the pressure-dependent yields of the OH and HO₂ product channels of the reaction CH₂OO + HNO₃ were evaluated in this work.

---

Footnotes:

Khan, M. A. H.; Percival, C. J.; Caravan, R. L.; Taatjes, C. A.; Shallcross, D. E. Environ. Sci.: Processes Impacts 2018, 20, 437–453.I Raghunath, P.; Lee, Y.-P.; Lin, M. C. J. Phys. Chem. A 2017, 121, 3871– 3878.H Luo, P.-L.; Horng, E.-C. Commun Chem 2020, 3, 95; Luo, P.-L. Opt. Lett. 2020, 45, 6791–6794.w