Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Aerosol particles composed of co-crystalline CO(2)·C(2)H(2) were generated in a bath gas cooling cell at cryogenic temperatures and investigated with infrared spectroscopy between 600 and 4000 cm(-1). Similar to results obtained for thin films of the co-crystal [T. E. Gough and T. E. Rowat, J. Chem. Phys. 109, 6809 (1998)], this phase was found to be metastable and decomposed into pure CO(2) and pure C(2)H(2). These decomposed aerosols were characterized through (i) a comparison to experimentally prepared aerosols of mixed CO(2) and C(2)H(2) of known architectures and (ii) the modeling of infrared spectra. A likely architecture after decomposition are C(2)H(2)-CO(2) core-shell particles with a disk-like shape. The co-crystalline CO(2)·C(2)H(2) aerosols prior to decomposition are modeled and analyzed in detail in the subsequent paper (Part II).     

Termolecular ion-molecule reactions in Titan’s atmosphere. II: The structure of the association adducts of HCNH+ with C2H2 and C2H4

The ion-molecule reactivity of the products formed in the association reactions of HCNH+ with C2H2 (C3H4N+) and C2H4 (C3H6N+) has been investigated to provide information on the structures of the adducts thus formed. The C3H4N+ and C3H6N+ adducts were formed in the reaction flow tube of a flowing afterglow sourced-selected ion flow tube (FA-SIFT) and their reactivity with a neutral molecular "probe" examined. The reactivity of possible known structural isomers for the C3H4N+ and C3H6N+ ions was investigated in both the FA-SIFT and an ion cyclotron resonance spectrometer (ICR). Ab initio investigations of the potential energy surfaces for both structures at the G2(MP2) level have also been performed and structures corresponding to local minima on both surfaces have been identified and evaluated. The results of these experimental and theoretical studies show that at room temperature, the C3H4N+ adduct ion contains two isomers; a less reactive one that is likely to be a four-membered cyclic covalent isomer (approximately 70%) and a faster reacting component that is probably an electrostatic complex (approximately 30%). The C3H6N+ adduct ion formed from HCNH+ + C2H4 at room temperature is a single isomer that is likely to be the four-membered covalently bound cyclic CH2CH2CHNH+ species.     

Molecular structure of finely disperse Na+Cl−(H2O) n aerosol particles in water vapor

The thermodynamic states corresponding to solvent separated (SSIP) and contacting (CIP) Na⁺Cl^? ion pairs in molecular water clusters have been obtained by random walks in a configurational space with an equilibrium distribution function at 273 and 150 K. The transition to the SSIP state begins in a thresh-old-type manner in clusters containing 10–12 molecules, with the interionic distance increasing continuously up to disintegration into two hydrated ions with the growth of a hydration shell. As the cluster size increases, the hydration shell shifts from sodium ion to chlorine ion. In the first hydration layer, the electric field of the ions ruptures as many as 50% of hydrogen bonds.     

Are vibrational relaxation times really constant? II. The vibrational relaxation of C2H2

Vibrational relaxation times of pure acetylene in the gas phase were measured behind incident shock waves in the temperature range 613–1184 K using a laser-schlieren technique. Overall, the results are in excellent agreement with those of acoustic and laser excitations. However, we find a marked intrinsic time dependence of the phenomenological time, which varies by factors of two to three over a wide dynamic time scale of at least six natural lifetimes. In other words, the Bethe—Teller law fails. This is confirmed by numerical solution of the master equation for a wide choice of intermode collisional coupling parameters. The density of states involved in the energy transfer process determines whether the relaxation time increases or decreases with time, and the effect is amplified by the importance of intermolecular VV processes relative to intramolecular processes.     

Palladium acetate complexes with morpholine and 4-methylmorpholine. The structure of Pd(C4H9ON)2(OAc)2 · 2H2O

Methods for the synthesis of new palladium(II) acetate complexes [L₂Pd(OCOCH₃)₂], where L is N-coordinated morpholine (C₄H₉ON) or 4-methylmorpholine (C₅H₁₁ON), have been developed. The structure of the complex (C₄H₉ON)₂Pd(OAc)₂ · 2H₂O (1) has been established by X-ray diffraction. The crystals of 1 are monoclinic (C₁₂H₂₆O₈N₂Pd, M = 434.76), space group P2(1)/c, a = 9.129(3) Å, b = 16.227(5) Å, c = 6.159(2) Å, V = 878.5(5) ų, Z = 2. The palladium atom has a square-planar environment with the trans arrangement of ligands. The complex (C₅H₁₁ON)₂Pd(OAc)₂ (2) has a similar structure, according to spectroscopic data.     

Infrared spectra of gaseous organics: Application to the atmosphere of Titan—II. Infrared intensities and frequencies of C4 alkanenitriles and benzene

The infrared spectra of butanenitrile (n-propyl cyanide = n-PrCN), 2-methylpropanenitrile (isopropyl cyanide = i-PrCN), cyclopropanecarbonitrile (cyclopropyl cyanide = ΔCN) and benzene, in the gas phase, have been systematically studied in the 3000-250 cm⁻¹ wavenumber region. For each of these compounds the most intense vibration bands have been determined. Their absolute intensities and the associated uncertainties have been estimated. These data were then used to derive upper limits of the mean mixing ratios of these compounds in Titan's atmosphere from a newly studied selection of IRIS i.r. spectra. The obtained upper limits are of the order of a few tenths of ppm for the studied nitriles and a few ppb for benzene.     

Infrared and infrared emission spectroscopy of nesquehonite Mg(OH)(HCO3)·2H2O-implications for the formula of nesquehonite

The mineral nesquehonite Mg(OH)(HCO(3))·2H(2)O has been analysed by a combination of infrared (IR) and infrared emission spectroscopy (IES). Both techniques show OH vibrations, both stretching and deformation modes. IES proves the OH units are stable up to 450°C. The strong IR band at 934 cm(-1) is evidence for MgOH deformation modes supporting the concept of HCO(3)(-) units in the molecular structure. Infrared bands at 1027, 1052 and 1098 cm(-1) are attributed to the symmetric stretching modes of HCO(3)(-) and CO(3)(2-) units. Infrared bands at 1419, 1439, 1511, and 1528 cm(-1) are assigned to the antisymmetric stretching modes of CO(3)(2-) and HCO(3)(-) units. IES supported by thermoanalytical results defines the thermal stability of nesquehonite. IES defines the changes in the molecular structure of nesquehonite with temperature. The results of IR and IES supports the concept that the formula of nesquehonite is better defined as Mg(OH)(HCO(3))·2H(2)O.     

Spectra and structure of organogermanes—XXIII. Infrared and Raman spectra of methylgermyl isothiocyanate

The mid i.r. spectra (3200-500 cm⁻¹) of gaseous and solid methylgermyl isothiocyanate and two of its isotopic derivatives, CD₃GeH₂NCS and CH₃GeD₂NCS, as well as the far i.r. spectra of the solids, have been recorded. The Raman spectra of the liquid and solid phases have also been obtained, and a relatively complete vibrational assignment has been made based on the i.r. band contours, Raman depolarization values, group frequencies and isotopic shifts. A number of depolarized Raman lines are observed which indicates that the GeNC angle is either pseudolinear or the NCS group is eclipsing the methyl carbon atom. No evidence could be found in the vibrational spectra for conformers. In the spectra of the solids, most of the fundamentals were observed as doublets which indicates that there are at least two molecules per primitive cell. The results of this study are compared to the corresponding data for the germyl pseudohalides and methylgermyl halides.     

The enthalpy of solution of MgCl2 and MgCl2·6H2O in water at 25°C. I. The integral molar enthalpy of solution

The data for the relative apparent and integral molar enthalpy of solution, L and H _sol ⁱⁿ , respectively, were critically reviewed, for the magnesium chloride-water system at 25°C. The concentration dependence L(m) and the enthalpy of solution at infinite dilution H _sol ^o were determined calorimetrically at 25°C. Both results are in agreement with most of the small amount of data published previously. From the results of our measurements, and from the most reliable value for H _sol ^o of MgCl₂, the concentration dependence H _sol ⁱⁿ (m) at 25°C was derived, for MgCl₂·6H₂O. The enthalpy of the hydration

Formation and structure of a Pd(I) complex: The crystal structure of (C5H8N2S)4Pd(II)Cl2·H2O and the ESR study of the X-irradiated single crystal

The crystal structure of tetrakis(tetrahydro-1H-pyrimidine-2-thione)palladium(II) dichloride monohydrate has been determined. X-irradiation of a single crystal, at liquid-nitrogen temperature, leads to formation of a paramagnetic species whose ESR study has been performed at 77 K. The g and ¹⁰⁵Pd-hyperfine tensors have been obtained. Their eigenvalues are consistent with the trapping of a d⁹ ion. Comparison of the eigenvectors with the crystallographic bond directions shows that the paramagnetic species results from the reduction of Pd(II) to Pd(I) which remains at the center of a square formed by four sulphur atoms.     

Crystal structure and magnetic behavior of Cu3(O2C16H23)6·1.2 C6H12. An unexpected structure and an example of spin frustration

A copper(II) carboxylate has been obtained from the reaction of basic copper carbonate, CuCO₃·Cu(OH)₂, with 2,4,6-triisopropylbenzoic acid. It contains a trinuclear Cu₃⁶⁺ core with three-fold symmetry, with each pair of copper atoms bridged by two carboxylate ligands. The Cu···Cu separations are 3.131(3) Å, precluding any direct bonding. Magnetic susceptibility data from 1.8 to 380 K at 1 000 G indicate a doublet ground state, (g ≈ 2.1) between 10–50 K (μ_eff = 1.80 μ_B). Above 50 K, the magnetic moment increases to 2.69 μ_B at 380 K, as expected for an equilateral triangular system of Cu^II with antiferromagnetic interactions between spin carriers.     

Synthesis and crystal structure of KBi(C6H4O7) · 3.5H2O

A novel compound, KBi(C₆H₄O₇) · 3.5H₂O (I), has been synthesized in the Bi(NO₃)₂-K₃(HCit) system (HCit^3? is an anion of citric acid C₆H₈O₇) at a component ratio (n) of 8 in a water-glycerol mixture, and its crystal structure has been determined. The crystals are unstable in air. The crystals are triclinic: a = 7.462 Å, b = 10.064 Å, c = 17.582 Å, α = 100.27°, β = 99.31°, γ = 105.48°, V = 1221.2 ų, Z = 2, space group $P\bar 1$ . In the structure of I, asymmetric binuclear fragments [Bi₂(Cit^4?)₂(H₂O)₂]^2? are linked through inversion centers into polymeric chain anions. Ions K⁺ and crystal water molecules are arranged in channels between the chains. The Bi(1)...Bi(2) distances in the binuclear fragment are 4.62 Å, and the Bi(1)...Bi(1) and Bi(2)...Bi(2) distances between bismuth atoms in the chain are 5.83 and 5.95 Å, respectively. The chains are linked through bridging oxygen atoms of the ligands Cit to form layers. In the centrosymmetric four-membered chelate ring Bi₂O₂ formed through Bi-O(Cit) bonds, the distances Bi(1)-Bi(1) are equal to 4.55 Å, and Bi(1)-O are 2.66 and 2.84 Å. The Bi-O bond lengths in I are in the range 2.12–3.16 Å. The Cit ligands act as hexadentate chelating/bridging ligands.     

The secondary thioamide function—II. The vibrational analysis of KOOCCSNHCH3, H2NCOCSNHCH3, and H2NCSCSNHCH3

The vibrational analysis of X-CSNHCH₃ (X  CONH₂, CSNH₂, COOK) and the N and C deuterated derivatives, has been proposed; the results have been compared with the data obtained for X-CSNHCH₃ X  H, CH₃, C₆H₅, CONHCH₃).Some general conclusions have been made about the secondary thioamide group.     

Molecular geometries of H2S···ICF3 and H2O···ICF3 characterised by broadband rotational spectroscopy

The rotational spectra of three isotopologues of H(2)S···ICF(3) and four isotopologues of H(2)O···ICF(3) are measured from 7-18 GHz by chirped-pulse Fourier transform microwave spectroscopy. The rotational constant, B(0), centrifugal distortion constants, D(J) and D(JK), and nuclear quadrupole coupling constant of (127)I, χ(aa)(I), are precisely determined for H(2)S···ICF(3) and H(2)O···ICF(3) by fitting observed transitions to the Hamiltonians appropriate to symmetric tops. The measured rotational constants allow determination of the molecular geometries. The C(2) axis of H(2)O/H(2)S intersects the C(3) axis of the CF(3)I sub-unit at the oxygen atom. The lengths of halogen bonds identified between iodine and sulphur, r(S···I), and iodine and oxygen, r(O···I), are determined to be 3.5589(2) ? and 3.0517(18) ? respectively. The angle, φ, between the local C(2) axis of the H(2)S/H(2)O sub-unit and the C(3) axis of CF(3)I is found to be 93.7(2)° in H(2)S···ICF(3) and 34.4(20)° in H(2)O···ICF(3). The observed symmetric top spectra imply nearly free internal rotation of the C(2) axis of the hydrogen sulphide/water unit about the C(3) axis of CF(3)I in each of these complexes. Additional transitions of H(2)(16)O···ICF(3), D(2)(16)O···ICF(3) and H(2)(18)O···ICF(3) can be assigned only using asymmetric top Hamiltonians, suggesting that the effective rigid-rotor fits employed do not completely represent the internal dynamics of H(2)O···ICF(3).