The 3ν1 + ν3 vibrational overtone spectrum of CH4

The 3 ν₁ + ν₃ vibrational overtone spectrum of ¹³CH₄ is recorded under Doppler-limited resolution conditions using a titanium sapphire laser-based photoacoustic spectrometer. Data at two temperatures, 100 and 293 K, are presented. The observed spectral congestion is qualitatively similar to that observed for ¹²CH₄, but the detailed ro-vibrational structure of the two isotope variants is completely different. The data reflect the complicating influences of tetrahedral fine structure and vibrational state mixing.     

The ν3 infrared spectrum of the He---NH4 complex

The mid-infrared spectrum of the ionic complex He---NH₄⁺ has been recorded in the vicinity of the triply degenerate ν₃ (t₂) vibration of the free ammonium ion. Apart from a small blue shift (≈ 0.7 cm⁻¹), the spectrum of the complex closely resembles that of the monomer. Ab initio calculations predict a vertex-bound minimum structure with an intermolecular well depth D_e ≈ 150 cm⁻¹, a center-of-mass separation of R_e ≈ 3.17 Å and barriers for internal rotation less than 30 cm⁻¹.     

Photofragmentation of CF3I in the A band

CF₃I is photodissociated in a molecular beam with 248 nm laser lighl. Fragmentation takes place into CF₃ and I(²P_3/2) or I(²P_1/2). The quantum yield for excited I (I* = I(²P_1/2)) formation is determined to be 0.92. The CF₃ fragments are found to be considerably vibrationally excited. Of the available energy in the CF₃ + I* channel 39% (0.69 eV) appears on the average as vibrational energy in the CF₃ radical. The angular distributions in both channels show predominantly parallel character. It can be concluded that at this wavelength 97% of the total absorption is due to the ³Q₀ ← ¹A₁ transition and only 3% to the ¹Q ← ¹A₁ transition. Most of the signal in the CF₃ + I channel originates from an effective crossing between the ³Q₀ and ¹Q states. A coupled channel calculation is performed to obtain a better insight into the dissociation dynamics of the CF₃I molecule. The results indicate that the CF₃ fragments from dissociation of CF₃I at 248 nm may be expected to be vibrationally excited. However, the experimental distribution has a higher average energy and is much broader. An explanation for this phenomenon is suggested.     

IR study on the intensity of ν1 of carbon disulfide

The IR intensity of ν₁ of carbon disulfide is reported in various states. The intensity increases with a decrease in temperature. Less than 10% of the observed intensity can be explained in terms of an electric field applied from an adjacent molecule. On the other hand, nearly half of the intensity is explained in terms of a vibrational coupling of ν₁ with ν₃ or ν₂, which is estimated from dimer models, on the assumption that the observed IR and Raman frequencies can be attributed to dimers.     

Diode laser spectroscopy of the ν8 band of the SF5Cl molecule

Diode laser spectra of SF(5)Cl have been recorded in the nu(8) band region at a temperature of ca. 240 K, a pressure of 0.25 mbar and an instrumental bandwidth of ca. 0.001 cm(-1). Four regions have been studied: a first one in the P-branch (906.849-907.687 cm(-1)), a second one in the Q-branch (910.407-910.944 cm(-1)), and two other ones in the R-branch (913.957-914.556 and 917.853-918.705 cm(-1) ). The whole nu(1)/nu(8) dyad of SF(5)35Cl has been previously recorded in the group of Professor H. Burger in Wuppertal, thanks to a Fourier transform infrared spectrometer. These data have thus been combined with our diode laser ones in the aim of refining the analysis. We used an effective Hamiltonian developed up to the fourth order and a set of programs called C(4nu)TDS. One thousand three hundred and forty-six transitions for nu(1), 495 (FTIR: 351; diode laser: 144) transitions for nu(8), and 406 ground state combination differences have been assigned and fitted. A global fit has been obtained with a rms of 0.00081 cm(-1) for the nu(1) band, 0.0012 cm(-1) for the FTIR data of the nu(8) band, 0.00055 cm(-1) for the diode laser data of this same band, and 0.00064 cm(-1) for the ground state. It appears that more data (for instance, using a supersonic jet) are still necessary to obtain a completely satisfactory analysis of the nu(8) region.     

Observation and rovibrational analysis of the ν2 band of HCN–HCl

The high-resolution infrared absorption spectrum of an equilibrium mixture of HCN and HCl in a static gas long-path absorption cell is recorded in the 2500–2900 cm⁻¹ spectral region at 205 K. The spectrum shows rovibrational structure which has the typical appearance of a parallel band of a linear molecule and is assigned to the intramolecular H–Cl stretching vibration band ν₂ of the linear HCN–H³⁵Cl heterodimer. The rovibrational analysis of the band yield a band origin ν₀ of 2779.0968(12) cm⁻¹ together with a value for the upper-state rotational constant B′ of 0.067722(2) cm⁻¹. The observed red shift of 107 cm⁻¹ for the ν₂ band of HCN–H³⁵Cl relative to the H–Cl stretching vibration band of monomer H³⁵Cl is in excellent agreement with results from the MP2/6−311++G** level of theory. The value of the upper-state rotational constant shows that the intermolecular hydrogen bond shortens by 0.022 Å upon intramolecular vibrational excitation of the ν₂ mode.     

Microwave spectrum of the hydroxyl radical in the ν= 1 Π3/2 state

The J = 7/2, 9/2, 11/2, 13/2 and 15/2 Λ doubling main lines of OH in the ν = 1, ² Π3/2 state have been measured. They are used with the UV and IR data to predict the low J frequencies with an accuracy sufficient for radioastronomical search.     

Synthesis and molecular structure of Ba5(μ5-OH)[μ3-OCH(CF3)2]4[μ2-OCH(CF3)2]4 [OCH(CF3)2](THF)4(H2O)·THF: a source of barium fluoride

The reaction between metallic barium and fluoroisopropanol or alcoholysis of [Ba(OPrⁱ)₂] produces a pentanuclear fluoroalkoxide. Its X-ray structure determination showed its formulation to correspond to Ba₅(μ₅-OH)[μ₃-OCH(CF₃)₂]₄[μ₂-OCH(CF₃)₂]₄ [OCH(CF₃)₂](THF)₄(H₂O)·THF. The metallic core is based on a square pyramid encapsulating an hydroxo ligand. In addition to the barium---alkoxide bonds [2.53(3)–2.86(3) Å] neutral O-donors, four THF [2.82(2)–2.86(3) Å] and one H₂O [2.79(3) Å] and secondary barium---fluorine interactions [2.99(2)–3.31(2) Å] ensure high coordination numbers, from 9 to 11 for the metal centers. Hydrogen bonding between the apical fluoroisopropoxide, the water molecule and one THF molecule, non-bonded to a metal center, accounts for the stability of the hydrate and illustrates the Lewis acidity of fluoroalkoxides. Thermal decomposition leads to BaF₂.     

Infrared dephasing of degenerate fundamentals: The ν6 mode of liquid CD3I

A model of vibrational dephasing with motional narrowing by the librational motions of the molecules in their cages is tested on the example of the ν₆ degenerate infrared fundamental of liquid CD₃l at room temperature.     

Vergleich der trifluormethylierungseigenschaften von(CF3)Hg,CF3I und (CF3)2te am beispiel der reaktionen mit cyclohexen,benzol und pyridin

The trifluoromethylation reactions of (CF₃)₂Hg, CF₃I and (CF₃)₂Te with cyclohexene, benzene and pyridine are compared under similar conditions. Photochemical as well as thermal reactions result in an increase of the reactivity in the series (CF₃)₂Hg < CF₃I ? (CF₃)2Te. The yields and the kind of products vary depending on the time of irradiation and the temperature. In all cases the best yields are obtained from the thermal reactions with (CF₃)₂Te. With cyclohexene only trifluoromethylated addition products are observed. The substitution reactions with pyridine yield a mixture of isomeric trifluoromethylpyridines. (CF₃)₂Hg and CF₃I react with benzene to yield only benzotrifluoride C₆H₅CF₃. The main product of the reaction of (CF₃)2Te with benzene is also benzotrifluoride; in addition to this the disubstituted bis(trifluoromethyl)benzene isomers and trifluoromethyl- cyclohexadienes are formed. ¹H, ¹⁹F n.m.r. and mass spectra are described.     

O- versus F-protonation in (CF3CF2)2O and CF3OCF(CF3)2: a preliminary theoretical study

The relative modifications induced in the structure of perfluorodiethyl ether (CF₃CF₂)₂O and perfluoroisopropyl methyl ether CF₃OCF(CF₃)₂ by oxygen and fluorine protonation are studied at the RHF level with the 3–21G basis and correlated with their proton affinities and dissociation energies.     

On the origin of the splittings of the ν3(SO4) modes in the specular reflectance IR spectra of gypsum

The IR polarized spectra of gypsum CaSO₄·2H₂O were recorded at incidence angles of approximately 10 and 16 degrees. Band singlet or doublet was observed for the higher frequency ν₃(SO₄²⁻) mode of B_u symmetry type, depending on polarization (n or p). A doublet was observed for the lower frequency ν₃(SO₄²⁻) mode of B_u symmetry type too, irrespectively of the type of polarization. In order to give an explanation for the doublets origin, a model permittivity function was constructed. Quite good agreement exists between the reflectance based on the model permittivity function and the experimentally measured one for the high-frequency doublet. The origin of the lower frequency doublet could not be explained in this way, but may be speculated to result from an Evans type interaction between a combination of a water libration and ν₂(SO₄²⁻), with the lower frequency ν₃(SO₄²⁻) mode.     

Direct dynamics studies on the hydrogen abstraction reactions CF3O+CH4(CD4)→CF3OH(CF3OD)+CH3(CD3)

The dynamics properties of the hydrogen abstraction reaction CF₃O+CH₄→CF₃OH+CH₃ are studied by dual-level direct dynamics method. Optimization calculations are preformed by B3LYP and MP2 with the 6-311G(d,p) basis set, and the single-point calculations are done at the multi-coefficient correction method based on quadratic configuration interaction with single and double excitations (MC-QCISD) method. The rate constants are evaluated by canonical variational transition-state theory with a small-curvature tunneling correction over a wide range of temperature 200–2000 K. The agreement between theoretical and experimental rate constants is good in the measured temperature range. The calculated results show that the variational effect is small and almost neglected over the whole temperature range, whereas, the tunneling correction plays a role in the lower temperature range. The kinetic isotope effect for the reaction is ‘normal’. The value of k_H/k_D is 2.38 at room temperature and it decreases with the temperature increasing.     

Experimental and theoretical study of the IR spectrum of [(CH2OH)3CNH3]2SiF6 crystal

[(CH₂OH)₃CNH₃]₂SiF₆, (tris(hydroxymethyl)aminomethane)₂SiF₆ crystal, abbreviated as (TRIS)₂SiF₆ crystal, exhibits a solid-solid phase transition (PT) at 182 K. The phase transition is connected with reorientational motion of SiF₆²⁻ and -CH₂OH groups. The vibrational infrared spectra of powdered (TRIS)₂SiF₆ crystal in Nujol and Fluorolube mulls were studied in the wide range of temperatures, from 320 K to 133 K. A wide region of internal vibrations of the TRIS⁺ and SiF₆²⁻ ions was investigated. Temperature changes of wavenumber, width, centre of gravity, and intensity of bands were analyzed to clarify the molecular mechanism of the phase transitions. Theoretical calculations were made based on density functional theory (DFT). The calculated normal vibrational modes of the molecules, their frequencies and intensities were compared with those obtained from experimental data.     

Comparative performance of CF3I,CD3I and CH3I in an atomic iodine photodissociation laser

We have compared the performance of CF₃I, CD₃I, and CH₃I in an atomic iodine photodissociation laser over the pressure range 1–200 torr. At pressures below 5 torr, CD₃I produces larger energy outputs, while above 5 torr CF₃I gives superior performance. The crossing of the laser energy output versus pressure curves is explained on the basis of collisional quenching of I(²P_{$\text{1}\text{2}$})(≡I^*) by undissociated alkyl iodide.     

C(CF3)2OH → OCH(CF3)2 Isomerism in some sulfur and phosphorus compounds

The insertion of (CF₃)₂CO into the PH bond of Me_nH_3?nP yields Me_nH_2?nPC(CF₃)₂OH and Me_nH_1?nP[C(CF₃)₂OH]₂ (n=O, 1), respectively [1]. MeP[C(CF₃)₂OH]₂ rearranges giving the diphosphine [MePOCH(CF₃)₂]₂ and the phosphorane MeP[OCH(CF₃)₂]₄. Me₂PH reacts with (CF₃)₂CO forming several products, e.g. MePF[OCH(CF₃)₂]₂ and Me₂PPMe₂ [1]. The phosphines tBu(R)PH(R=Me, tBu), however, add (CF₃)₂CO giving rise to the phosphinites tBu(R)POCH(CF₃)₂, which furnish stable phosphonium salts upon treating with MeI. (CF₃)₂CO inserts into the SH bond of RSH to yield RSC(CF₃)₂OH (R=H,Me,Ph), which were reacted with MeI, too. Reacting SCl₂ with LiOCH(CF₃)₂ gives S[OCH(CF₃)₂]₂ which is oxidised by chlorine to the sulfurane ClS[OCH(CF₃)₂]₃ [2]. The sulfurane is able to transfer (CF₃)₂CHO groups to phosphorus (III) compounds, e.g. P[OCH(CF₃)₂]₃ and Me₃P yielding P[OCH(CF₃)₂]₅ and [Me₃POCH(CF₃)₂]⁺Cl^?. ClS[OCH(CF₃)₂]₃ gives a stable salt upon reaction with SbCl₅, like ClP[OCH(CF₃)₂]₄. The mechanisms for these reactions are discussed.     

Untersuchungen zum reaktiven verhalten von (CF3)2PPH2 und (CF3)2AsPH2

Cleavage of the E-P bond in compounds of the type (CF₃)₂EPh₂(E = P, As) is achieved by polar [HBr, (CF₃)₂EI, (CH₃)₃SnH, (CF₃)₂AsH] and non-polar [Br₂, Mn₂(CO)₁₀] substances. Exchange reactions are possible with (CF₃₄)E₂ and P₂F₄ leading to the unsymmetrical compounds (CF₃)₂PPF₂, (CF₃)₂AsPF₂, (CF₃)₂PAs(CF₃)₂, F₂PPH₂, (CF₃)₂AsPH₂. The reaction of (CF₃)₂PPH₂ with Mn₂(CO)₁₀ gives the new binuclear complex Mn₂(CO)₈PH₂P(CF₃)₂ and Mn₂(CO)₈[P(CF₃)₂]₂. The hitherto unknown compound (CF₃)₂AsPF₂ is obtained by the reaction of (CF₃)₂AsPH₂ with P₂F₄. Adducts of (CF₃)₂PPH₂ with B₂H₆ and (CH₃)₃N, respectively, are discussed. Investigation of the reaction route and characterization of most of the reaction product is based on ¹H and ¹⁹F NMR spectral data.     

The syntheses and mass spectra of P[CCCF3]3, As[CCCF3]3, and Sb[CCCF3]3

The syntheses of P[CCCF₃]₃, As[CC CF₃]₃, and Sb[CCCF₃]₃ are reported. The compounds are colorless and volatile, with melting points of ?20° to ?25°, 23–24°, and 55–56°C, respectively. The mass spectra show the molecular ion of each compound. The rearrangement ion [F₃CCCCCCF₂]⁺] gives the strongest peak in each spectrum.     

Perfluormethyl-element-liganden : XXXI. Ligandeneigenschaften von Me2PP(CF3)2 und Me2AsP(CF3)2

The coordinating properties of the trifluoromethyl elemental compounds Me₂PP(CF₃)₂ and Me₂AsP(CF₃)₂ have been studied by the synthesis and spectroscopic investigations (IR, NMR, MS) of their complexes cis-M(CO)₄L₂ (A), [(CO)₄ML]₂ (B) and [(CO)₅M]₂L (C) (M = Cr, Mo, W). Complexes of type A with L = Me₂PP(CF₃)₂ are obtained in good yield by reaction with M(CO)₄NBD (NBD = norbornadiene), whereas with L = Me₂AsP(CF₃)₂ the homobinuclear compounds B are formed. The attempt to prepare the cis-M(CO)₄[Me₂AsP(CF₃)₂]₂ complexes by treating M(CO)₄(Me₂AsH)₂ with P₂(CF₃)₄ is successful only for M = W. Binuclear compounds of type B or C, in general, can be prepared by stepwise reaction of the ligands with either M(CO)₄NBD or M(CO)₅THF.