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High resolution FTIR spectra of 13C enriched tetrafluoroethylene (C2F4) were measured at 150 K at the Australian Synchrotron. Rovibrational transitions were assigned in the a-type symmetric and b-type antisymmetric CF2 stretches of 12C13CF4 and 13C2F4 near 1170 cm-1 and 1300 cm-1, respectively. Ground vibrational state spectroscopic constants for both molecules were determined in addition to the upper state constants for ν11 and ν9 of 13C2F4 and ν11, ν2+ν6, and ν5 of 12C13CF4. The ground state constants, along with those determined for the 12C2F4 isotopologue from previously published data, were used to determine a semi-experimental re structure rCC = 132.36 ± 0.37 pm, rCF = 131.11 ± 0.23 pm, αFCC = 123.3 ± 0.3° in excellent agreement with ab initio structures. Lower resolution FTIR spectra were measured between 100 and 5000 cm-1 at room temperature and band centres obtained for all modes of the three isotopologues; although only 5 out of 12 modes in 12C2F4 and 13C2F4 are infrared (IR) active, the others were inferred from combination and hot-band positions. A number of modes are observed to be infrared active only in the 12C13CF4 isotopologue due to its lower symmetry. Most notably, decoupling of the antisymmetric CF2 motions in the two halves of 12C13CF4 results in 2 strongly IR active modes that involve motion at one carbon or the other. [ABSTRACT FROM AUTHOR]

The recent detection of a chiral molecule, propylene oxide, in the interstellar medium provides impetus for investigation of related analogues as candidates for discovery of a second chiral species. Vinyloxirane (VO) shares many of the characteristics of propylene oxide that favored its remote detection such as modest size, appreciable dipole moment and modest adsorption to water ice. The microwave spectrum of vinyloxirane at room temperature has been studied in the 18 - 26 GHz region. Rotational transitions of the previously undetected gauche -1 conformer have been assigned and fitted. The quantum number range of anti conformer transitions has been greatly expanded, providing improved molecular constants. Vibrational satellite transitions were assigned and fitted for the lowest frequency ν 27 torsion mode, for 2ν 27 , and for the ν 26 C=CC bend of anti VO, along with ν 27 satellites of gauche -1. The rovibrational analyses were assisted by anharmonic vibrational calculations at B3LYP-D3/aug-cc-PVTZ, B2PLYPD3/cc-pVTZ, and DSDPBEP86/cc-pVTZ levels. Experimental peak intensities provide a population ratio N gauche-1 / N anti of 0.36 ± 0.06, corresponding to a Gibbs free energy difference of 2.5 ± 0.4 kJ mol -1 in favor of the anti , is optimized at -35° to favor an intramolecular C gauche -1 conformer, the torsional angle between vinyl group and oxirane ring, τ C=CCM , is optimized at -35° to favor an intramolecular C vinyl H 11 of + 74° suffers from C gauche -2 conformer with τ C=CCM of + 74° suffers from C vinyl H 11 ...HC cyclopropyl repulsion so that it is calculated to be 8-9 kJ mol -1 higher than gauche -1. Reinterpretation of earlier Raman spectra suggests that the gauche -2 conformer had not been observed as reported.

Broadband microwave spectra have been recorded between 7.0 and 18.5 GHz for N -methylimidazole⋯H 2 O and 2-methylimidazole⋯H 2 O complexes. Each complex was generated by co-expansion of low concentrations of methylimidazole and H 2 O in argon buffer gas. The rotational spectra of five isotopologues of each complex have been assigned and analysed to determine rotational constants ( A 0 , B 0 , C 0 ), centrifugal distortion constants ( D J , D JK ) and parameters that describe the internal rotation of the CH 3 group. The results allow the determination of parameters in the ( r 0 ) molecular geometry of each complex. H 2 O is the hydrogen bond donor and the pyridinic nitrogen of imidazole is the hydrogen bond acceptor in each case. The ∠(O-H b ⋯N3) angles are 177(5)° and 166.3(28)° for N -methylimidazole⋯H 2 O and 2-methylimidazole⋯H 2 O respectively. These results are consistent with the presence of a weak electrostatic interaction between the oxygen atom of H 2 O and the hydrogen atom (or CH 3 group) attached to the C2 carbon atom of imidazole, and with the results of density functional theory calculations. The ( V 3 ) barrier to internal rotation of the CH 3 group within N -methylimidazole⋯H 2 O is essentially unchanged from the value of this parameter for the N -methylimidazole monomer. The same parameter is significantly higher for the 2-methylimidazole⋯H 2 O complex than for the 2-methylimidazole monomer as a consequence of the weak electrostatic interaction between the O atom and the CH 3 group of 2-methylimidazole.

The rotational spectra of N-, 2-, 4-, and 5-methylimidazole are reported and analyzed. Liquid N-methylimidazole was vaporized from a reservoir, and each of 2-, 4-, and 5-methylimidazole was laser-vaporized from a solid target prior to mixing with argon buffer gas and undergoing supersonic expansion from a pulsed nozzle. The spectra were recorded by chirped-pulse Fourier transform microwave spectroscopy in the 7.0-18.5 GHz frequency range. Rotational constants, A 0 , B 0 , and C 0 , centrifugal distortion constants, D J , D JK , D K , d 1 , and d 2 , and nuclear quadrupole coupling constants of nitrogen atoms, χ aa (N1), χ bb (N1) - χ cc (N1), χ aa (N3), and χ bb (N3) - χ cc (N3), are determined from experimentally measured transition frequencies. Data recorded for isotopologues containing 13 C or 15 N are used to determine the r s coordinates of all heavy atoms in N-, 2-, and 4-methylimidazole. The results allow fitting of parameters in the Hamiltonian that describes internal rotation of the CH 3 group about its local C 3 axis. The V 3 terms in the periodic potential energy functions that describe the internal rotation in N-, 2-, 4-, and 5-methylimidazole are determined to be 185.104(11), 122.7529(38), 317.20(14), and 386.001(19) cm -1 , respectively, by the internal axis method. The experiments are supported by density functional theory calculations. Observed variations in barrier height are explained with reference to the symmetry of overlap between a π-like orbital on the CH 3 group and π-orbitals on the aromatic ring.

Rotational spectra have been measured and assigned for four conformers of trans-urocanic acid. The acid was transferred into the gas phase through laser vaporisation of a solid sample, mixed with a neon buffer gas and then cooled through supersonic expansion. Molecules and complexes in the expanding gas jet were probed through chirped-pulse, Fourier transform microwave spectroscopy between 2.0 and 18.5 GHz. Rotational constants, A0, B0 and C0; centrifugal distortion constants, ΔJ and ΔJK; and nuclear quadrupole coupling constants of the nitrogen atoms, χaa(N) and χbb(N)-χcc(N), were determined for the various conformers. Data were obtained for ten isotopologues of the conformer that was observed to yield the spectrum of highest intensity. Substitution (rs) coordinates were determined for all carbon atoms and two hydrogen atoms of this conformer. Other observed spectra were assigned to conformers on the basis of excellent agreement between calculated and experimentally-determined rotational constants, and empirical observations of the relative intensities of a- and b-type transitions. The results of DFT calculations imply high barriers to the interconversion of assigned conformers.

Ground-state rotational spectra were observed for ten symmetric-top isotopologues H 3 N⋯S=C=S, H 3 N⋯ 34 S=C=S, H 3 N⋯S=C= 34 S, H 3 N⋯S= 13 C=S, H 3 N⋯S=C=S, H 15 N⋯S=C=S, H 3 S=C=S, H 15 N⋯S=C= 34 S=C=S, H 3 15 C=S, H 34 S, H 3 S=C=S, and H 15 N⋯S=C= 13 C=S, H 3 15 N⋯ 33 DN⋯S=C=S, H 3 15 S=C=S, H 33 DN⋯S=C= 15 NH 3 N⋯S=C=S were investigated by using a sample composed of ND 2 DN⋯S=C=S, H 2 DN⋯ 34 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 2 DN⋯S=C= 34 N⋯S=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 2 N⋯S=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 N⋯S=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 σ = 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(N⋯S) = 3.338(10) Å.

Ice and solid H 2 S look as different as pears and oranges, leading Pauling to conclude that H 2 O has hydrogen bonds and H 2 S has van der Waals interactions. Now it is shown that the H 2 S dimer, like the H 2 O dimer, is indeed hydrogen-bonded., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The rotational spectra of H 3 N⋯AgI and H 2 O⋯AgI have been recorded between 6.5 and 18.5 GHz by chirped-pulse Fourier-transform microwave spectroscopy. The complexes were generated through laser vaporisation of a solid target of silver or silver iodide in the presence of an argon gas pulse containing a low concentration of the Lewis base. The gaseous sample subsequently undergoes supersonic expansion which results in cooling of rotational and vibrational motions such that weakly bound complexes can form within the expanding gas jet. Spectroscopic parameters have been determined for eight isotopologues of H 3 N⋯AgI and six isotopologues of H 2 O⋯AgI. Rotational constants, B 0 ; centrifugal distortion constants, D J , D JK or Δ J , Δ JK ; and the nuclear quadrupole coupling constants, χ aa (I) and χ bb (I) - χ cc (I) are reported. H 3 N⋯AgI is shown to adopt a geometry that has C 3v symmetry. The geometry of H 2 O⋯AgI is C s at equilibrium but with a low barrier to inversion such that the vibrational wavefunction for the v = 0 state has C 2v symmetry. Trends in the nuclear quadrupole coupling constant of the iodine nucleus, χ aa (I), of L⋯AgI complexes are examined, where L is varied across the series (L = Ar, H 3 N, H 2 O, H 2 S, H 3 P, or CO). The results of experiments are reported alongside those of ab initio calculations at the CCSD(T)(F12*)/AVXZ level (X = T, Q).

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, χ aa (X) and χ bb (X)-χ cc (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 CH 3 X and CF 3 X.

The shapes of macromolecules and their complexes with small molecules are often determined by extended networks of hydrogen bonds. Here, for the first time, we provide a detailed description of a cooperative pair of hydrogen bonds to an individual molecule of urea. The structure and properties of a gas phase complex formed between urea and isocyanic acid are characterised through microwave spectroscopy and ab initio calculations at the CCSD(T)(F12*)/aug-cc-pVTZ level.

Complexes formed between H 2 S and each of CuI, AgI, and AuI have been isolated and structurally characterised in the gas phase. The H 2 S⋯MI complexes (where M is the metal atom) are generated through laser vaporisation of a metal rod in the presence of a low concentration of H 2 S and CF 3 I in a buffer gas of argon undergoing supersonic expansion. The microwave spectra of six isotopologues of each of H 2 S⋯CuI, H 2 S⋯AgI and three isotopologues of H 2 S⋯AuI have been measured by chirped-pulse Fourier transform microwave spectroscopy. The spectra are interpreted to determine geometries for the complexes and to establish the values of structural parameters. The complexes have C s symmetry at equilibrium and have a pyramidal configuration about the sulfur atom. The local C 2 axis of the hydrogen sulfide molecule intersects the linear axis defined by the three heavy atoms at an angle, ϕ = 75.00(47)° for M = Cu, ϕ = 78.43(76)° for M = Ag, and ϕ = 71.587(13)° for M = Au. The trend in the molecular geometries is consistent with significant relativistic effects in the gold-containing complex. The force constant describing the interaction between the H 2 S and MI sub-units is determined from the measured centrifugal distortion constant, Δ J , of each complex. Nuclear quadrupole coupling constants, χ aa (M) and χ aa (I) (where M denotes the metal atom), are determined for H 2 S⋯CuI and H 2 S⋯AuI for the first time.

Dispersion interactions are omnipresent in intermolecular interactions, but their respective contributions are difficult to predict. Aromatic ethers offer competing docking sites for alcohols: the ether oxygen as a well known hydrogen bond acceptor, but also the aromatic π system. The interaction with two aromatic moieties in diphenyl ether can tip the balance towards π binding. We use a multi-spectroscopic approach to study the molecular recognition, the structure and internal dynamics of the diphenyl ether-methanol complex, employing infrared, infrared-ultraviolet and microwave spectroscopy. We find that the conformer with the hydroxy group of the alcohol binding to one aromatic π cloud and being coordinated by an aromatic C-H bond of the other phenyl group is preferred. Depending on the expansion conditions in the supersonic jet, we observe a second conformer, which exhibits a hydrogen bond to the ether oxygen and is higher in energy.

Conformational flexibility is intrinsically related to the functionality of biomolecules. Elucidation of the potential energy surface is thus a necessary step towards understanding the mechanisms for molecular recognition such as docking of small organic molecules to larger macromolecular systems. In this work, we use broadband rotational spectroscopy in a molecular jet experiment to unravel the complex conformational space of citronellal. We observe fifteen conformations in the experimental conditions of the molecular jet, the highest number of conformers reported to date for a chiral molecule of this size using microwave spectroscopy. Studies of relative stability using different carrier gases in the supersonic expansion reveal conformational relaxation pathways that strongly favour ground-state structures with globular conformations. This study provides a blueprint of the complex conformational space of an important biosynthetic precursor and gives insights on the relation between its structure and biological functionality.

Molecular recognition of carbohydrates plays an important role in nature. The aggregation of the smallest sugar, glycolaldehyde, was studied in a conformer-selective manner using high-resolution rotational spectroscopy. Two different dimer structures were observed. The most stable conformer reveals C2 -symmetry by forming two intermolecular hydrogen bonds, giving up the strong intramolecular hydrogen bonds of the monomers and thus showing high hydrogen bond selectivity. By analyzing the spectra of the (13) C and (18) O isotopologues of the dimer in natural abundance, we could precisely determine the heavy backbone structure of the dimer. Comparison to the monomer structure and the complex with water provides insight into intermolecular interactions. Despite hydrogen bonding being the dominant interaction, precise predictions from quantum-chemical calculations highly rely on the consideration of dispersion., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

broadband microwave spectroscopy is a proven tool to precisely determine molecular properties of gas-phase molecules. Recent developments make it applicable to investigate chiral molecules. Enantiomers can be differentiated, and the enantiomeric excess and, indirectly, the absolute configuration can be determined in a molecule-selective manner. The resonant character and high resolution of rotational spectroscopy provide a unique mixture compatibility. Future directions, such as extending the technique to chemical analysis, are discussed.

The rotational spectrum of trans-cinnamaldehyde ((E)-3-phenyl-2-propenal, C9H8O) was recorded by chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 2-8.5 GHz. The odourant molecule is the essential component of cinnamon oil and causes the characteristic smell. The rotational signatures of two conformers were observed: s-trans-trans- and s-cis-trans-cinnamaldehyde. The rotational spectra of s-trans-trans-cinnamaldehyde and all of its (13)C-monosubstituted species in natural abundance were assigned and the corresponding carbon backbone structure was determined. The second conformer s-cis-trans-cinnamaldehyde is about 9 kJ mol(-1) higher in energy and could also be identified in the spectrum.

We apply chirality sensitive microwave three-wave mixing to 4-carvomenthenol, a molecule previously uncharacterized with rotational spectroscopy. We measure its rotational spectrum in the 2-8.5 GHz range and observe three molecular conformers. We describe our method in detail, from the initial step of spectral acquisition and assignment to the final step of determining absolute configuration and enantiomeric excess. Combining fitted rotational constants with dipole moment components derived from quantum chemical calculations, we identify candidate three-wave mixing cycles which were further tested using a double resonance method. Initial optimization of the three-wave mixing signal is done by varying the duration of the second excitation pulse. With known transition dipole matrix elements, absolute configuration can be directly determined from a single measurement.

Five intense bands of dichlorodifluoromethane (CFC-12, or R12) in the infrared atmospheric window help make it a major greenhouse contributor. These include the ν1 fundamental at 1101.4 cm(-1) and the ν2 + ν3 combination at 1128.6 cm(-1). High-resolution spectra measured using the Australian Synchrotron Far-Infrared beamline were analyzed, and transitions of C(35)Cl2F2 were assigned to ν1, ν2 + ν3, and the ν3 + 2ν5 combination at 1099.7 cm(-1). The (v3 = 1; v5 = 2) state couples indirectly to v1 = 1 via Fermi resonances linking both states with v2 = v3 = 1. The v1 = 1 rotational levels are further riddled with perturbations and avoided crossings due to Coriolis resonance with the upper vibrational states of ν2 + ν9 at 1102.4 cm(-1) and (indirectly) ν2 + ν7 at 1105.8 cm(-1). A global treatment of all these states fits the observed line positions and satisfactorily accounts for the significant intensity of ν2 + ν3. Spectral simulations elucidate resonance perturbations that affect the distribution of IR absorption in the CF stretch region, and consequently the global warming potential of R12. Combination levels derived from rovibrational analysis lead to reassessment of the gas phase wavenumber values for the ν3 (458.6 cm(-1)), ν7 (437.7 cm(-1)) and ν9 (436.9 cm(-1)) fundamentals of C(35)Cl2F2, consistent with a cold, vapor phase far IR spectrum and previously published solid state spectra. B3LYP and MP2 anharmonic frequency calculations provide further support. At the MP2/aug-cc-pVTZ level, the root mean square (r.m.s.) error for unscaled anharmonic fundamentals is 6.2 cm(-1), decreased to 1.7 cm(-1) if only considering the seven lowest wavenumber modes, and integrated band intensities according with experimental literature values. Smaller basis sets produce band strengths that are too high. Low-resolution band assignments are reported for C(35)Cl(37)ClF2, C(37)Cl2F2, and (13)C(35)Cl2F2.

Heavy-metal containing chiral compounds have been suggested as promising candidates for studying parity-violation effects. We report herein the broadband rotational spectroscopy study of the chiral complex [CpRe(CH3)(CO)(NO)] in the gas phase. The spectra obtained are very rich due to the two rhenium isotopologues ((185)Re and (187)Re), hyperfine structure arising from the rhenium and nitrogen nuclei, and the asymmetry of the chiral complex. Since rhenium is located very close to the molecular center of mass, the rotational constants for the two rhenium isotopologues are very similar. However they can be differentiated by their characteristic nuclear quadrupole hyperfine splitting patterns. Comparison with calculated nuclear quadrupole coupling constants shows that all-electron relativistic basis sets are necessary for a correct description of the rhenium atom in this type of complex. The present study is an important step towards future precision studies on chiral molecules., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Compared to ethylene and its nonfluorinated derivatives, C(2)F(4) is peculiar in many reactions. It very easily adds to radicals and prefers formation of four-membered rings over Diels-Alder reactions. This has been rationalized by the preference of fluorine for carbon sp(3) hybridization, which is possible on opening of the double bond. Another property, the thermal dissociation of the C ═ C bond, has been explained by the stabilization of the product (CF(2)) by back-bonding. Here, it is attempted to correlate such properties with vibrational constants, in particular for C ═ C stretching and twisting and for carbon pyramidalization. The only force constant found to be lowered compared to ethylene is that for trans pyramidalization (ν(8)), and CC bond softening on ν(8) distortion is indicated by the conspicuously large magnitude of anharmonic constant, x(18). Both observations can be rationalized by a valence-bond model that predicts a trans bent structure on weakening the CC bond. Conclusions are drawn about the dissociation path and peculiarities of the potential. Other anharmonicities, both experimental and calculated and some in (12)C(13)CF(4) and (13)C(2)F(4), are also discussed. In particular some strong Fermi resonances are identified and their effects accounted for.

The IR spectrum of dichlorodifluoromethane (i.e., R12 or Freon-12) is central to its role as a major greenhouse contributor. In this study, high-resolution (0.000 96 cm(-1)) Fourier transform infrared spectra have been measured for R12 samples either cooled to around 150 K or at ambient temperature using facilities on the infrared beamline of the Australian Synchrotron. Over 14,000 lines of C(35)Cl2F2 and C(35)Cl(37)ClF2 were assigned to the b-type ν2 band centered around 668 cm(-1). For the c-type ν8 band at 1161 cm(-1), over 10,000 lines were assigned to the two isotopologues. Rovibrational fits resulted in upper state constants for all these band systems. Localized avoided crossings in the ν8 system of C(35)Cl2F2, resulting from both a direct b-axis Coriolis interaction with ν3 + ν4 + ν7 and an indirect interaction with ν3 + ν4 + ν9, were treated. An improved set of ground state constants for C(35)Cl(37)ClF2 was obtained by a combined fit of IR ground state combination differences and previously published millimeter wave lines. Together these new sets of constants allow for accurate prediction of these bands and direct comparison with satellite data to enable accurate quantification.

Mid-infrared spectra have been measured for cubic ice (I(c)) nanoparticles (3-150 nm diameter) formed by rapid collisional cooling over a wide range of temperatures (5-209 K). Spectral diagnostics, such as the ratio of surface related dangling OH to interior H-bonded OH stretch bands, reveal the manner in which particle size depends on bath gas temperature and density, and on water molecule concentration. For particles smaller than 5 nm strained intermolecular bonds on the surface and subsurface cause the predominant OH stretch peak position to be dramatically blue shifted by up to 40 cm(-1). In the size regime of 8-200 nm the position of the OH stretch absorption band maximum is relatively unaffected by particle size and it is possible to measure the temperature dependence of the peak location without influences from the surface or scattering. The band maximum shifts in a linear fashion from 3218 cm(-1) at 30 K to 3253 cm(-1) at 209 K, which may assist with temperature profiling of ice particles in atmospheric clouds and extraterrestrial systems. Over the same temperature range the librational mode band shifts very little, from 870 to 860 cm(-1). In the water stretching and bending regions discrete spectral features associated with the surface or sub-surface layers have been detected in particles as large as 80 nm.

High resolution FTIR spectra of the short lived species ketenimine have been recorded in the regions 390-1300 cm(-1) and 20-110 cm(-1) using synchrotron radiation. Two thousand six hundred sixty transitions of the ν(7) band centered at 693 cm(-1) and 126 far-IR rotational transitions have been assigned. Rotational and centrifugal distortion parameters for the ν(7) mode were determined and local Fermi and b-axis Coriolis interactions with 2ν(12) are treated. A further refinement of the ground state, ν(12) and ν(8) parameters was also achieved, including the treatment of previously unrecognized ac-axis and ab-axis second order perturbations to the ground state., (© 2011 American Institute of Physics)

Aerosols of ozone have been generated in a collisional cooling cell and observed over a small temperature range via FTIR spectroscopy, with the phase transition from the vapour taking place in the range 80-84 K. The condensed phase bands at 1038 cm(-1) (nu3) and 2105 cm(-1) (nu1+nu3) were assigned to the liquid phase. Aerosols were also generated from mixtures of ozone and HCl. In the presence of liquid ozone aerosols, evidence of solvated HCl was observed via a broad IR band 2795 cm(-1). Notably, production of a metastable, amorphous solid phase of HCl (exhibiting a narrow band at 2780 cm(-1)) was favoured to the extent that it could be generated in large excess over the crystalline orthorhombic form that usually dominates at 80 K.

Aerosol particles of hydrogen chloride corresponding to three distinct solid phases have been generated in a collisional cooling cell and observed via FTIR spectroscopy. The cubic phase of HCl was observed with cell temperatures of 90-100 K, while the highly ordered orthorhombic phase predominated below this temperature. The previously reported metastable phase was also observed under some conditions. Density functional theory calculations at the B3LYP/6-311+G(d,p) level were performed on HCl clusters with a planar, zig-zag arrangement. Computed IR spectra for chain lengths up to 15 converge to show a band shape that is characteristic of the orthorhombic HCl phase. Injection of water along with HCl was found to have little influence on the formation of HCl particles. The reaction between HCl and NH3 to produce NH4Cl particles was also examined and found to occur over a wide range of temperatures (80-300 K). The formation of homogenous particles of HCl and NH3 competed with this chemical reaction as the cell temperature was lowered and when higher pressures of N2 buffer gas were used.