Rotational structure of small 4He clusters seeded with HF, HCl, and HBr molecules

Diffusion Monte Carlo calculations are performed for ground and excited rotational states of HX(4He)N, complexes with N相似文献   

Dipole and quadrupole moment functions of the hydrogen halides HF, HCl, HBr, and HI: a Hirshfeld interpretation

The dipole and quadrupole moment functions of the hydrogen halides are calculated using a large polarized basis and correlated wavefunctions and compared to experiment and previous calculations. These functions are analyzed in terms of local moments constructed using the Hirshfeld method. The dipole moment is the sum of the functions q(H)R+mu(H) and mu(X) with q(H) being the charge on the hydrogen atom, R the internuclear separation, mu(H) and mu(X) the atomic dipoles on the hydrogen and halogen atoms. We find that q(H)R+mu(H) is always positive and has a maximum at bond lengths larger than the equilibrium. In HF, mu(F) is slightly positive at the maximum in q(H)R+mu(H) and has little effect on the resultant maximum in the dipole moment function (DMF). mu(Cl), mu(Br), and mu(I), on the other hand, are increasingly more negative at the maximum of q(H)R+mu(H) and have a profound effect on the width of the maximum of the resulting DMF, successively broadening it and completely eliminating it at HI. The quadrupole moment function (QMF) (with the halogen as origin) is given by Theta(HX)=Theta(HX) (proto)+deltaTheta(X)+deltaTheta(H)+2mu(H)R+q(H)R(2), where Theta(HX) (proto) is the quadrupole moment of the separated atoms (the halogen in this instance) and deltaTheta(X)+deltaTheta(H) the change in the in situ quadrupole moments of the halogen and hydrogen atoms. The maximum in the QMF and its slope at equilibrium are determined essentially by 2mu(H)R+q(H)R(2), which is known once the DMF is known. deltaTheta(X)+deltaTheta(H) is always negative while Theta(HX) (proto) is positive, so one can approximate the molecular quadrupole moment to within 10% as Theta(HX)>Theta(HX) (proto)+2mu(H)R+q(H)R(2).     

Green's function calculations on the complete valence ionization spectra of HF,HCl, HBr AND HI

The ionization spectra of the entire valence region are calculated for HF, HCl, HBr and HI. For the two ionization processes of lowest energy the common molecular orbital picture of ionization applies, whereas this picture breaks down for ionization from the inner valence α-orbital. For HF and HCl basis set effects on the calculated outer-valence ionization energies are investigated and accurate values are computed using large basis sets. The calculated inner valence ionization spectra are compared with recent (e, 2e)-measurements.     

Study of the reactions of OH with HCl,HBr, and HI between 298 K and 460 K

The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be k_HCl(298 K) = (7.9 ± 1.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ with a weak positive temperature dependence, k_HBr (298-460 K) = (1.04 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_HI(298 K) = (3.0 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The homogeneous nature of these reactions has been experimentally tested.     

Unimolecular elimination of HF and HCl from chemically activated CF3CFClCH2Cl

The unimolecular reactions of CF3CFClCH2Cl molecules formed with 87 kcal mol(-1) of vibrational energy by recombination of CF3CFCl and CH2Cl radicals at room temperature have been characterized by the chemical activation technique. The 2,3-ClH and 2,3-FH elimination reactions, which have rate constants of (2.5 +/- 0.8) x 10(4) and (0.38 +/- 0.11) x 10(4) s(-1), respectively, are the major reactions. The 2,3-FCl interchange reaction was not observed. The trans (or E)-isomers of CF3CFCHCl and CF3CClCHCl are favored over the cis (or Z)-isomers. Density functional theory at the B3PW91/6-31G(d',p') level was used to evaluate thermochemistry and structures of the molecule and transition states. This information was used to calculate statistical rate constants. Matching the calculated to the experimental rate constants for the trans-isomers gave threshold energies of 62 and 63 kcal mol(-1) for HCl and HF elimination, respectively. The threshold energy for FCl interchange must be 3-4 kcal mol(-1) higher than for HF elimination. The results for CF3CFClCH2Cl are compared to those from CF3CFClCH3; the remarkable reduction in rate constants for HCl and HF elimination upon substitution of one Cl atom for one H atom is a consequence of both a lower E and higher threshold energies for CF3CFClCH2Cl.     

Absolute rate constants for the reactions O(3P) atoms with HCl and HBr

A flow tube method has been used to determine rate constants for the elementary reactions: Oxygen atoms were produced by adding a small excess of NO to a stream of partially dissociated nitrogen, and their reaction with hydrogen halide was monitored by observing the intensity of the NO + O afterglow. Experiments were carried out at temperatures from 293 to 440°K with HCl, and from 267 to 430°K with HBr. The role of secondary reactions was minimised and the residual effects were allowed for. The rate constants for the primary reactions could be matched by Arrhenius expressions: where the units are cm³/molec·sec and the errors correspond to a standard deviation.     

Spectrophotometric determination of pipazethate HCl, dextromethorphan HBr and drotaverine HCl in their pharmaceutical preparations

A simple, accurate and highly sensitive spectrophotometric method is proposed for the rapid determination of pipazethate hydrochloride, dextromethorphan hydrobromide and drotaverine hydrochloride using chromotrope 2B (C2B) and chromotrope 2R (C2R). The method consists of extracting the formed ion-associates into chloroform in the case of pipazethate HCl and dextromethorphan HBr or into methylene chloride in the case of drotaverine HCl. The ion-associates exhibit absorption maxima at 528, 540 and 532 nm with C2B and at 526, 517 and 522 nm with C2R for pipazethate HCl, dextromethorphan HBr and drotaverine HCl, respectively. The calibration curves resulting from the measurements of absorbance-concentration relations (at the optimum reaction conditions) of the extracted ion-pairs are linear over the concentration range 4.36-52.32 microg mL(-1) for pipazethate, 3.7-48.15 microg mL(-1) for dextromethorphan and 4.34-60.76 microg mL(-1) for drotaverine, respectively. The effect of acidity, reagent concentration, time, solvent and stoichiometric ratio of the ion-associates were estimated. The molar absorptivity and Sandell sensitivity of the reaction products were calculated. Statistical treatment of the results reflects that the procedure is precise, accurate and easily applied for the determination of the drugs under investigation in pure form and in their pharmaceutical preparations.     

Competition between HF And HCl molecular elimination in IRMPD of 1,2-dichloro-1,2-difluoroethane

The infrared multiple-photon decomposition of 1,2-dichloro-1,2-difluoroethane has been studied using time-resolved infrared emission. Vibrationally excited parent molecules dissociate competitively via two channels to form vibrationally excited HCl and HF, depending strongly on CO₂ laser fluence. The yield of HF elimination increases with fluence, while that of HCl elimination reaches a plateau and then decreases.     

Effect of vibrational excitation of HBr on the H+HBr abstraction and exchange reactions

The effect of vibrational excitation of HBr on the H+HBrH₂+Br and H+HBrH+HBr reactions has been investigated on the extended LEPS surface (ELEPS) constructed on the basis of quantum chemically calculated points of PES. Together with this surface the LEPS surface of Sudhakaran and Raff [1] was used for comparison at two relative translational energies. A quasiclassical trajectory method was used to study the abstraction and exchange reaction dynamics. The reactive cross section was calculated as a function of the relative collision energy and the vibrational state of HBr. The following conclusions can be drawn from the results of the study: (i) vibrational excitation v=0 v=2 more than doubles the reaction cross section, (ii) the increase in the collision energy is most effectively channelled into the product translational energy.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

Topological analysis of transition states of the concerted molecular decomposition of haloalkanes and alcohols with HHal and HOH elimination

The quantum chemical modeling and topological analysis of transition states of the concerted molecular decomposition of haloalkanes and alcohols with the elimination of HHal and HOH were performed for the ten compounds. The possibility of formation of two types of transition states was mentioned, and their electronic structures were studied. The influence of the alkyl substituent at the C atoms on the binding energy and the nature of the transition state was shown. The decomposition activation energies were calculated using the method of density functional theory (DFT/B3LYP/6-311++G**) and the intersecting parabolas method. The calculated results were compared, and their agreement was shown.     

Model potential calculations for HF and HCl

A model potential method proposed recently by the present authors has been tested successfully for HF and HCl. Calculated values of total energies, orbital energies and spectroscopic constants are quite acceptable.     

Thermocatalytic transformations of wood and cellulose in the presence of HCl, HBr, and H2SO4

The compositions of the liquid organic products formed from aspen wood and cellulose at 150, 200, and 250° C in the presence of 1, 3, and 5% of HCl, HBr, and H₂SO₄ have been studied. The yield of levulinic acid from wood reached 13.0–15.5%, and from cellulose 28.8%.Institute of the Chemistry of Natural Organic Raw Material, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, fax (3912) 43 93 42. Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 107–112, January–February, 1997.     

Detection of HCl and HF by TTFMS and WMS

In this work we discuss on a compact spectrometer based on DFB diode lasers for detection of chloridric and fluoridric acids. HCl and HF concentrations are determined through optical absorption of the P(4) line (lambda=1.7 microm) and the R(3) line (lambda=1.3 microm), respectively. Both lines belong to first overtone vibrational bands and their line strengths are 7.8 x 10(-21)cm/molecule for HCl and 2.8 x 10(-20)cm/molecule for HF. We chose these lines for their relative high intensities and because they are quite far from water vapour lines which represent the main interfering gas for trace-gases analysis. To detect these species we used two different high frequency modulation techniques: two-tone frequency modulation spectroscopy (f(1)=800 MHz and f(2)=804 MHz) was used for HCl while for HF we followed a simpler approach based on wavelength modulation spectroscopy (f=600 kHz). We demonstrate that the two techniques provide comparable detection limit of about 80 ppbV at atmospheric pressure. Positive testing of our spectrometer makes it suitable for in situ measurements of exhaust gases coming from waste incinerators.     

Thermal electron attachment processes in gas mixtures containing H2S,HCl and HBr

The kinetics of thermal electron capture reactions by H₂S, HCl and HBr in mixtures with CO₂ have been investigated using the electron swarm method. A mechanism involving van der Waals molecules (H₂S)₂, (HCl·CO₂) and (HBr·CO₂) has been proposed and the rate constants have been calculated. Some tentative conclusions have been made concerning the influence of electronegativity and the dipole moment of the electron scavenger on the mechanism of the electron capture process.     

Capillary complexation gas chromatography in analysis of halohydrocarbons

Summary Investigations were carried out on capillary columns coated with liquid stationary phases possessing cyano (3-cyanopropylmethylpolysiloxane) and thiol (3-mercaptopropylmethylpolysiloxane) groups. These phases were modified by bonding CuCl₂ and CoCl₂ to cyano groups or NiCl₂ and CoCl₂ to thiol groups. The modified phases were examined in order to assess their usefulness for the analysis of aliphatic and aromatic halohydrocarbons. A number of retention parameters (I, ΔMe, Vg), which allow characterisation of the specific interactions between the bonded metal and the halohydrocarbon molecule, were determined for the columns both with and without the metal. The separations performed show that the columns with bonded metals are applicable for the practical analysis of the halohydrocarbons.