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1.
J Phys Chem A ; 114(14): 4748-54, 2010 Apr 15.
Article in English | MEDLINE | ID: mdl-20050594

ABSTRACT

Limiting low- and high-pressure rate coefficients as well as full falloff curves have been modeled by unimolecular rate theory for the recombination reaction 2CF(3) (+ M) --> C(2)F(6) (+ M) and the reverse dissociation of C(2)F(6). The results are compared with experimental data from the literature. Although there are considerable discrepancies (up to a factor of 5) between various experimental data near 300 K and the database for high temperatures is still limited, we try to conclude on the temperature dependence of the high-pressure rate coefficient. We suggest that there is only a small and probably positive temperature coefficient of the latter quantity. The present theoretical modeling seems to be in agreement with this experimental result, but it is in disagreement with conclusions from earlier theoretical work. The difference is attributed to different empirical assumptions about the anisotropy of the potential. It is shown that nearly all previous experiments (except high-temperature shock wave and very low pressure pyrolysis/photolysis experiments) correspond to nearly limiting high-pressure conditions.


Subject(s)
Chlorofluorocarbons, Methane/chemistry , Fluorocarbons/chemistry , Pressure , Temperature , Kinetics , Models, Chemical
2.
Rev Sci Instrum ; 80(11): 113106, 2009 Nov.
Article in English | MEDLINE | ID: mdl-19947716

ABSTRACT

We introduce a beam profiler of pulsed lasers based on the photoacoustic technique. The method assumes that the initial pressure distribution inside the acoustic cell follows the laser intensity pattern if absorbed energy relaxes rapidly. This initial pressure condition can be described as a superposition of acoustic modes of different amplitudes and phases. We analyze how to reconstruct the intensity profile of the laser beam from the recorded acoustic signals. Finally, we present preliminary results obtained with a frequency doubled Nd:YAG laser that excites NO(2)-CF(2)Cl(2) mixtures.


Subject(s)
Acoustics , Lasers, Solid-State , Chlorofluorocarbons, Methane/chemistry , Equipment Design , Laboratories , Nitrogen Dioxide/chemistry , Signal Processing, Computer-Assisted
3.
J Phys Chem A ; 113(52): 14818-23, 2009 Dec 31.
Article in English | MEDLINE | ID: mdl-19670828

ABSTRACT

We have studied systems with typical hydrogen bonding and others with interaction involving hydrogen. CH(4)-CH(4), CH(4)-H(2)O, CHF(3)-CH(4), and CHF(3)-H(2)O dimers were studied using MPWB1K, PBE1PBE, MP2, and QCISD levels of theory with a large number of basis functions. The Pople 6-31+G(2d), 6-311++G(2d,2p), and 6-311++G(3df,3pd) as well as Dunning augmented aug-cc-pVDZ and aug-cc-pVTZ basis sets were used. The dimer geometries were fully optimized. An optimal basis set was determined for these systems to achieve a suitable compromise between accuracy and computational feasibility. A proper strategy was found for the electronic property calculations of dimers studied: the use of aug-cc-pVDZ as the optimal basis set at MP2 level. Dipole moments, polarizabilities, BSSE effects, and DeltaZPE were also analyzed for these dimers.


Subject(s)
Chlorofluorocarbons, Methane/chemistry , Dimerization , Methane/chemistry , Quantum Theory , Water/chemistry , Models, Molecular , Molecular Conformation , Thermodynamics
4.
J Phys Chem A ; 112(27): 6211-6, 2008 Jul 10.
Article in English | MEDLINE | ID: mdl-18547036

ABSTRACT

Trifluorothioacetic acid-S-(trifluoromethyl)ester, CF3C(O)SCF3, was prepared by reacting CF3C(O)Cl and AgSCF3 at 50 degrees C. The compound was characterized by (13)C-, (19)F-NMR, UV, and vibrational spectroscopy as well as by gas electron diffraction (GED) and quantum chemical calculations (HF, MP2, and B3LYP methods 6-31G(d) and 6-311+G(2df) basis sets). GED and vibrational spectroscopy result in the presence of a single conformer with C1 symmetry and synperiplanar orientation of the S-CF3 bond relative to the CO bond. This result is in agreement with quantum chemical calculations which predict the anti conformer to be higher in energy by about 4 kcal/mol. An assignment of the IR (gas) and Raman (liquid) spectra is proposed, and the GED analysis results in the following skeletal geometric parameters (r(a) and angle(a) values with 3sigma uncertainties; these parameters are thermal averages and are not inconsistent with calculated equilibrium values): C=O = 1.202(6) A, C-C = 1.525(10) A, S-C(sp(2)) = 1.774(3) A, S-C(sp(3)) = 1.824 (3) A. O=C-C = 118.7(21) degrees, O=C-S = 127.1(15) degrees, C-S-C = 99.8 (13) degrees.


Subject(s)
Chlorofluorocarbons, Methane/chemistry , Esters/chemistry , Sulfhydryl Compounds/chemistry , Esters/chemical synthesis , Molecular Conformation , Molecular Structure , Quantum Theory , Spectrum Analysis
5.
Article in English | MEDLINE | ID: mdl-11206559

ABSTRACT

The polar tensors of CF3Cl, CF2Cl2 and CFCl3 have been calculated using recent measurements of their gas phase infrared fundamental intensities. The polar tensors obtained for CF2Cl2 and CFCl3 are in very good agreement with those obtained previously since the more recent experimental intensity results are in good agreement with those reported earlier. For CF2Cl2 rhoC = +1.626, rhoF = -0.577 and rhoCl = -0.26e whereas rhoC = +1.369, 0.478 and rhoCl = 0.297e for CFCl3. However, two sets of significantly different mean dipole moment derivatives are obtained from the experimentally measured intensities of CF3Cl reported by two different laboratories. On the other hand, the differences in the mean derivatives of these two sets are not large enough so that results from electronegativity models, potential models for core ionization energies and quantum chemical calculations at the Moller-Plesset 2 and B3LYP density functional levels are sufficient to indicate which set is the correct one. As such average values of rhoC = +1.907+/-0.178e, rhoF = -0.590+/-0.056e and rhoCl = -0.139+/-0.013e obtained from both sets of polar tensor elements are recommended for the CF33Cl mean dipole moment derivatives.


Subject(s)
Chlorofluorocarbons, Methane/chemistry , Electrochemistry , Software
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