The pure rotational spectra of Ar−AuCl and Kr−AuCl have been measured using a pulsed-jet cavity Fourier transform microwave spectrometer. Both complexes have been found to be linear and are relatively rigid in their ground vibrational states. The noble gas−gold stretching frequencies have been estimated to be 198 and 161 cm-1 for Ar−AuCl and Kr−AuCl, respectively. From the isotopic data obtained, r 0 structures have been calculated for both Ar−AuCl and Kr−AuCl, while a partial substitution (r s) structure has been obtained for Kr−AuCl. The Ar−Au distance has been found to be 2.47 Å, while the Kr−Au distance is 2.52 Å. Ab initio calculations have been performed at the MP2 level of theory on both complexes to obtain geometries, vibrational frequencies, and dissociation energies. The dissociation energies for Ar−AuCl and Kr−AuCl have been estimated to be 47 and 71 kJ mol-1, respectively. The nuclear quadrupole coupling constant of Au has been found to change significantly on complex formation (to −259.8 MHz in Ar−AuCl, and −349.9 MHz in Kr−AuCl) from its value in the monomer unit (+9.6 MHz in AuCl), which is consistent with extensive charge rearrangement on formation of the complexes. This, in conjunction with the sizable dissociation energies, indicates that the Ar−Au and Kr−Au bonds are weakly covalent.

Abstract.A degradation mechanism for β-caryophyllene has recently been released as part of version 3.2 of the Master Chemical Mechanism (MCM v3.2), describing the gas phase oxidation initiated by reaction with ozone, OH radicals and NO 3 radicals. A detailed overview of the construction methodology is given, within the context of reported experimental and theoretical mechanistic appraisals. The performance of the mechanism has been evaluated in chamber simulations in which the gas phase chemistry was coupled to a representation of the gas-to-aerosol partitioning of 280 multi-functional oxidation products. This evaluation exercise considered data from a number of chamber studies of either the ozonolysis of β-caryophyllene, or the photo-oxidation of β-caryophyllene/NO x mixtures, in which detailed product distributions have been reported. This includes the results of a series of photo-oxidation experiments performed in the University of Manchester aerosol chamber, also reported here, in which a comprehensive characterization of the temporal evolution of the organic product distribution in the gas phase was carried out, using Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), in conjunction with measurements of NO x , O 3 and SOA mass loading. The CIR-TOF-MS measurements allowed approximately 45 time-resolved product ion signals to be detected, which were assigned on the basis of the simulated temporal profiles of the more abundant MCM v3.2 species, and their probable fragmentation patterns. The evaluation studies demonstrate that the MCM v3.2 mechanism provides an acceptable description of β-caryophyllene degradation under the chamber conditions considered, with the temporal evolution of the observables identified above generally being recreated within the uncertainty bounds of key parameters within the mechanism. The studies have highlighted a number of areas of uncertainty or discrepancy, where further investigation would be valuable to help interpret the results of chamber studies and improve detailed mechanistic understanding. These particularly include: (i) quantification of the yield and stability of the secondary ozonide (denoted BCSOZ in MCM v3.2), formed from β-caryophyllene ozonolysis, and elucidation of the details of its further oxidation, including whether the products retain the "ozonide" functionality; (ii) investigation of the impact of NO x on the β-caryophyllene ozonolysis mechanism, in particular its effect on the formation of β-caryophyllinic acid (denoted Published by Copernicus Publications on behalf of the European Geosciences Union. M. E. Jenkin et al.: Development and chamber evaluation of the MCM v3.2 degradation schemeC137CO2H in MCM v3.2), and elucidation of its formation mechanism; (iii) routine independent identification of β-caryophyllinic acid, and its potentially significant isomer β-nocaryophyllonic acid (denoted C131CO2H in MCM v3.2); (iv) more precise quantification of the primary yield of OH (and other radicals) from β-caryophyllene ozonolysis; (v) quan...

The rotational spectra of the complexes Ar–CuF, Ar–CuCl, and Ar–CuBr have been observed in the frequency range 5–22 GHz using a pulsed-jet cavity Fourier transform microwave spectrometer. All the complexes are linear and rather rigid in the ground vibrational state, with the Ar–Cu stretching frequency estimated as ∼200 cm−1. Isotopic data have been used to calculate an r0 structure for Ar–CuF, while for Ar–CuCl and Ar–CuBr partial substitution structures have also been obtained. To reduce zero-point vibrational effects a double substitution method (rd) has also been employed to calculate the structures of Ar–CuCl and Ar–CuBr. The Ar–Cu distance has been found to be rather short and to range from 2.22 Å in Ar–CuF to 2.30 Å in Ar–CuBr. Ab initio calculations at the MP2 level of theory model the geometries and stretching frequencies well and predict an Ar–Cu bond energy in Ar–CuF of ∼47.3 kJ mol−1. Large changes in the Cu nuclear quadrupole coupling constant on complex formation show that extensive charge rearrangement occurs upon formation of the complexes. This, in conjunction with the sizable dissociation energy, suggests that the Ar–Cu bonds in these complexes are weakly covalent. The rotational spectrum of CuF has also been reinvestigated to improve the hyperfine constants.

The rotational spectra of the complexes Ar–AgF, Ar–AgCl, and Ar–AgBr have been observed in the frequency range 6–20 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. All the complexes are linear and rather rigid in the ground vibrational state, with the Ar–Ag stretching frequency estimated as ∼140 cm−1. Isotopic data have been used to calculate an r0 structure for Ar–AgF, while for Ar–AgCl and Ar–AgBr partial substitution structures have also been obtained. To reduce zero-point vibrational effects a double substitution method (rd) was employed to calculate the structures of Ar–AgCl and Ar–AgBr. The Ar–Ag bond distance has been found to be rather short and to range from 2.56 Å in Ar–AgF to 2.64 Å in Ar–AgBr. Ab initio MP2 and density functional theory calculations for Ar–AgF and Ar–AgCl model the geometries and stretching frequency well, and predict an Ar–Ag bond energy in Ar–AgF of ∼23 kJ mol−1. These results indicate that the Ar–AgX complexes are more strongly bound than typical van der Waals complexes. Analysis of the halogen nuclear quadrupole coupling constants was unable to confirm whether extensive electron rearrangement occurs upon formation of the complexes.

No abstract