Cavity Ring-down UV spectroscopy of the C2Σ+^2\Sigma^+-X2Π^2\Pi electronic transition of CH

Rotationally resolved spectra of the C$^2\Sigma^+$-X$^2\Pi$ electronic system of the CH radical were measured using cavity ring-down spectroscopy in supersonically expanding, planar hydrocarbon plasma. The experimental conditions allowed the study of highly excited rotational levels starting from vibrationally excited states. Here we present some 200+ new or more accurately recorded transitions in the 0-0, 1-1 and 2-2 vibronic bands in the ultraviolet between 30900-32400 cm$^{-1}$ (324-309 nm). The resulting data, compared to earlier measurements, allows for the determination of more precise molecular constants for each vibrational state and therefore more precise equilibrium values. From this an equilibrium bond length of 1.115798(17) \r{A} for the C$^2{\Sigma}^+$ state is determined. A comprehensive list with observed transitions for each band has been compiled from all available experimental studies and constraints are placed on the predissociation lifetimes

Halogen bonding vs hydrogen bonding in CHF2I complexes with NH3 and N(CH3)3

Ammonia and trimethylamine (TMA) were used to probe preference of hydrogen over halogen bonding in molecular complexes containing CHF$_2$I via chirped pulse Fourier transform microwave spectroscopy. The halogen bonded complex of TMA is $\approx$ 2 kJ/mol more energetically favourable (extrapolation to CCSD(T)/CBS level) than the hydrogen bonded complex. The reverse is true for the ammonia complex where the hydrogen bonded complex is $\approx$ 3kJ/mol more favourable. Although the spectra of both complexes were perturbed by large amplitude motions around the intermolecular bond effective fits of the lower rotational energy levels appear to confirm that TMA prefers to bind to the iodine whilst ammonia prefers the hydrogen

Letter from W. G. Medcraft as well as a letter of recommendation from W. F. Hoyl

Letter concerning a position in the mathematics department at Utah Agricultural College, as well as a recommendation

BROADBAND FTMW SPECTROSCOPY OF THE UREA-ARGON AND THIOUREA-ARGON COMPLEXES

The rotational spectra complexes of argon-urea, argon-thiourea and water-thiourea have been measured by chirped-pulse Fourier transform microwave spectroscopy from 2-18.5 GHz. The sample was produced via laser vaporisation of a rod containing copper and the organic sample as a stream of argon was passed over the surface and subsequently expanded into the vacuum chamber cooling the sample. Argon was found to bind to $pi$ system of the carbonyl bond for both the urea and thiourea complexes

Microwave spectroscopy and structure determination of H2S − MI (M=Cu,Ag,Au)

A series of hydrogen sulphide-metal iodide complexes (\chem{H_2S}-MI, M$=$Cu, Ag and Au) have been measured via chirped pulse Fourier transform microwave spectroscopy between 7.5-18 GHz. The complexes were generated in a supersonic expansion via laser ablation of the metal and decomposition of CF$_3$I. Experimental structures were obtained by least squares fitting of structural parameters to the rotational constants of deuterium and metal ($^{63}$Cu / $^{65}$Cu and $^{107}$Ag / $^{109}$Ag) isotopologues. Interestingly K$_{-1}$=1 transitions were observed in the spectra containing D$_2$S, these were not observed in previous studies of similar molecules (H$_2$S-MCl). This allowed for the determination of an extra rotational constant and, consequently, extra structural information could be obtained. The structures are compared to high level coupled cluster theory calculations

A K-BAND MICROWAVE SPECTROMETER FOR STUDYING ATMOSPHERIC REACTIONS

A segmented Chirped Pulse Fourier Transform Microwave (CP-FTMW) spectrometer has recently been installed in the Molecular Photonics Laboratories at UNSW Sydney. It covers the K-band (18-26 GHz) with an 18 MHz per segment bandwidth. This frequency range permits probing samples at room temperature and in a supersonic expansion. The stable products of atmospheric oxidation reactions of biological and anthropogenic volatile organic carbons (VOCs) will probed in a room temperature cell. Reactive and transient species will be probed in a supersonic expansion using a custom discharge mixing nozzle. The nozzle combines a standard high voltage discharge source with a secondary source introduced into the expansion via a capillary gas line. This secondary source is pulsed to reduce gas load and improve sample density. Performance and preliminary results will be presented along with supporting \textit{ab initio} calculations

BROADBAND FTMW SPECTROSCOPY OF 2-METHYLIMIDAZOLE AND COMPLEXES WITH WATER AND ARGON

The rotational spectrum of 2-methylimidazole has been measured using laser ablation chirped-pulse Fourier transform microwave spectroscopy from 2-18.5 GHz. 2-methylimidazole was laser vaporised then entrained within an argon buffer gas undergoing supersonic expansion allowing for efficient rotational cooling. Carbon-13 and nitrogen-15 isotopologues were measured in natural abundance and substitution coordinates have been determined. The barrier to internal rotation of the methyl group was found to be 122.697(20) cm$^{-1}$. Nuclear quadropole coupling constants for the two nitrogen nuclei were determined via a rigid rotor fit of the $A$ internal rotor state. Complexes with water and argon were also observed and fit in a similar way

Halogen bonding properties of 4-iodopyrazole and 4-bromopyrazole explored by rotational spectroscopy and ab initio calculations

The combination of halogen- and hydrogen-bonding capabilities possessed by 4-bromopyrazole and 4-iodopyrazole has led to them being described as "magic bullets" for biochemical structure determination. Laser vaporisation was used to introduce each of these 4-halopyrazoles into an argon gas sample undergoing supersonic expansion prior to the recording of the rotational spectra of these molecules by chirped-pulse Fourier transform microwave spectroscopy. Data were obtained for four isotopologues of 4-bromopyrazole and two isotopologues of 4-iodopyrazole. Isotopic substitutions were achieved at the hydrogens attached to the pyrrolic nitrogen atoms of both 4-halopyrazoles and at the bromine atom of 4-bromopyrazole. The experimentally determined nuclear quadrupole coupling constants, χaa(X) and χbb (X)-χcc (X), of the halogen atoms (where X is the halogen atom) of each molecule are compared with the results of the ab initio calculations and those for a range of other halogen-containing molecules. It is concluded that each of 4-bromopyrazole and 4-iodopyrazole will form halogen bonds that are broadly comparable in strength to those formed by CH3X and CF3X

A chalcogen-bonded complex H₃N⋅⋅⋅S=C=S formed by ammonia and carbon disulfide characterised by chirped-pulse, broadband microwave spectroscopy

Ground-state rotational spectra were observed for ten symmetric-top isotopologues H 3 NS=C=S, H 3 N 34 S=C=S, H 3 NS=C= 34 S, H 3 NS= 13 C=S, H 3 15 NS=C=S, H 3 15 N 34 S=C=S, H 3 15 NS=C= 34 S, H 3 15 NS= 13 C=S, H 3 15 N 33 S=C=S, and H 3 15 NS=C= 33 S, the first five in their natural abundance in a mixture of ammonia and carbon disulphide in argon and the second group with enriched 15 NH 3 . The four asymmetric-rotor isotopomers H 2 DNS=C=S, H 2 DN 34 S=C=S, H 2 DNS=C= 34 S, and HD 2 NS=C=S were investigated by using a sample composed of ND 3 mixed with CS 2 . Rotational constants, centrifugal distortion constants, and 33 S nuclear quadrupole coupling constants were determined from spectral analyses and were interpreted with the aid of models of the complex to determine its symmetry, geometry, one measure of the strength of the intermolecular binding, and information about the subunit dynamics. The complex has C 3v symmetry, with nuclei in the order H 3 NS=C=S, thereby establishing that the non-covalent interaction is a chalcogen bond involving the non-bonding electron pair of ammonia as the nucleophile and the axial region near one of the S atoms as the electrophile. The small intermolecular stretching force constant k ¿ = 3.95(5) N m -1 indicates a weak interaction and suggests the assumption of unperturbed component geometries on complex formation. A simple model used to account for the contribution of the subunit angular oscillations to the zero-point motion leads to the intermolecular bond length r(NS) = 3.338(10) Å. © 2019 Author(s).We thank Newcastle University for a research studentship (for E.G.), the University of Bristol for a Senior Research Fellowship (for A.C.L.), and the Australian Research Council for a Discovery Early Career Research Fellowship (No. DE180101194) (for C.M.). The authors thank the Engineering and Physical Sciences Research Council (UK) and the European Research Council for funding construction of the instrument used for this work (under Grant Nos. EP/G026424/1 and CPFTMW-307000, respectively).Peer Reviewe