Infrared spectra of the C2H2-(OCS)2 van der Waals complex: observation of a structure with C2 symmetry

Infrared spectra of the C(2)H(2)-(OCS)(2) trimer are studied by means of direct infrared absorption spectroscopy. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser in the region of the ν(1) fundamental vibration of the OCS monomer. Two infrared bands are analyzed for the lowest energy isomer of the trimer, which has C(2) symmetry and is experimentally observed here for the first time. A relatively strong band centered at 2068.93 cm(-1) is assigned as the out-of-phase vibrations of the pair of equivalent OCS monomers. This band is blue-shifted relative to the free OCS monomer but with a reduced shift as compared with the analogous vibration of the nonpolar OCS dimer. A weaker red-shifted band observed at 2049.64 cm(-1) establishes the nonplanarity of the OCS dimer subunit within the trimer. Spectra for three isotopologues in addition to the normal form are used to help define an experimental structure, which agrees well with past and present semiempirical calculations.     

Infrared spectrum and structural assignment of the water trimer anion

The bending vibrational spectrum of the perdeutero isotopomer of the water trimer anion has been measured and compared with spectra calculated using the MP2, CCSD, and Becke3LYP electronic structure methods. Due to its low electron binding energy (approximately 150 meV), only the OD bending region of the IR spectrum of (D2O)3(-) is accessible experimentally, with electron ejection dominating at higher photon energies. The calculated spectrum of the isomer having three water molecules arranged in a chain agrees best with the experimental spectrum. In the chain isomer, the excess electron is bound to the terminal water monomer with two dangling OH groups. This is consistent with the electron binding mechanism established previously for the (H2O)n(-) (n = 2, 4-6) anions.     

Spectroscopic observation and structure of CS2 dimer

Infrared spectra of the CS(2) dimer are observed in the region of the CS(2) ν(3) fundamental band (～1535 cm(-1)) using a tunable diode laser spectrometer. The weakly bound complex is formed in a pulsed supersonic slit-jet expansion of a dilute gas mixture of carbon disulfide in helium. Contrary to the planar slipped-parallel geometry previously observed for (CO(2))(2), (N(2)O)(2), and (OCS)(2), the CS(2) dimer exhibits a cross-shaped structure with D(2d) symmetry. Two bands were observed and analyzed: the fundamental (C-S asymmetric stretch) and a combination involving this mode plus an intermolecular vibration. In both cases, the rotational structure corresponds to a perpendicular (ΔK = ±1) band of a symmetric rotor molecule. The intermolecular center of mass separation (C-C distance) is determined to be 3.539(7) A?. Thanks to symmetry, this is the only parameter required to characterize the structure, if the monomer geometry is assumed to remain unchanged in the dimer. From the band centers of the fundamental and combination band an intermolecular frequency of 10.96 cm(-1) is obtained, which we assign as the torsional bending mode. This constitutes the first high resolution spectroscopic investigation of CS(2) dimer.     

Infrared spectrum and structure of 2-thienyl-N-methylfulleropyrrolidine

The IR and ¹H NMR spectra of 2-thienyl-N-methylfulleropyrrolidine are studied. The complete interpretation of the spectra is carried out on the basis of density functional theory calculations. Conformational composition is analyzed by means of both computational and experimental methods.     

Infrared spectrum and structure of CH2=ThH2

The actinide methylidene CH2=ThH2 molecule is formed in the reaction of laser-ablated thorium atoms with CH4 and trapped in a solid argon matrix. The five strongest infrared absorptions computed by density functional theory (two ThH2 stretches, C=Th stretch, CH2 wag, and ThH2 bend) are observed in the infrared spectrum. The computed structure shows considerable agostic bonding distortion of the CH2 and ThH2 subunits in the simple actinide methylidene dihydride CH2=ThH2 molecule, which is similar to the transition metal analogue, CH2=HfH2.     

Infrared spectra of the OCS trimer

Infrared spectra of the barrel-shaped trimer (OCS)(3), previously known from its microwave spectrum, are reported for the first time. The observations are carried out in a supersonic slit-jet expansion of a He+OCS gas mixture which is probed with a tunable diode laser. Three rotationally resolved bands associated with the nu(1) fundamental vibration of OCS (2062.20 cm(-1)) are observed, at about 2047, 2053, and 2077 cm(-1). Small perturbations are noted in the 2077 cm(-1) band and may also be present in the 2053 cm(-1) band, which is weak and hence more difficult to analyze precisely. Employing a variety of evidence, we suggest a plausible assignment for the nature of the OCS vibrations in each of the three bands.     

Finding the 3D structure of a molecule in its IR spectrum

 The labile iron(II) and iron(III) species are complexed directly in the sample solution with 1,10 phenanthroline and ferron (8-hydroxy-7-iodoquinoline-5-sulfonic acid), respectively. The complexes thus formed are mutually adsorbed and separated by solid phase extraction. The direct determination of iron(III) and iron(II) species with flame atomic absorption spectrometry (FAAS) follows the elution of the iron(III)-ferron complex adsorbed by an anion-exchange and an iron(II)-phenanthroline complex adsorbed by a non-polar RP-18 phase. In the case of indirect determination, the iron(II)-phenanthroline complex that passes through the anion-exchange phase, is measured, and the content of iron(III) is calculated by the difference of the iron(II) and the total iron content. A direct determination with this method has been applied to the iron species analysis in wine samples and the results are compared with those obtained for the determination with adsorptive stripping voltammetry (ASV) as reference method. Received: 17 August 1995/Revised: 12 February 1996/Accepted: 14 February 1996     

Pseudorotation in the D2O trimer

Far-infrared spectra of Ar/D2O supersonic expansions have been recorded between 39 and 44 cm-1, in which a c-type band centered at 41.1 cm-1 was observed. This new band, attributed to the cyclic water trimer, has the same ground state rotational constants as the (D20)3 98 cm-1 a-type band reported by Liu et al. [J. Am. Chem. Soc. 116 (1994) 3507]. Fits of the observed far-infrared band positions to an effective one-dimensional potential require a substantially larger pseudorotation barrier or effective moment of inertia than predicted theoretically. Estimated frequencies of unobserved transitions in the pseudorotation manifolds of (D2O)3 and (H20)3 are presented as a guide to future experimental searches.     

Electronic structure of H2CS3 and H2CS4: an experimental and theoretical study

The HeI photoelectron spectra of H2CS3 and H2CS4 in the gas phase have been obtained for the first time. A complete theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) and population analysis was performed. Calculations of cation-radical forms were carried out in order to interpret the main characters of the six highest occupied molecular orbitals (HOMOs). The first vertical ionization potentials are 8.74 and 8.56eV for H2CS3 and H2CS4, and attributed to {9b2(nS(C=S))}-1 and {8a"(3ppi*(S-S), nS)}-1, respectively. Meanwhile, the energy sequence of three types of sulfur 3p lone-pair have been discussed: 3ppi(S-S)*相似文献   

Analysis of the normal modes of molecules with D3h symmetry: Infrared spectra of monomeric s-triazine and cyanuric acid

Normal modes of s-triazine and cyanuric acid were calculated at the DFT(B3LYP)/6-311++G(d,p) level. These modes were analyzed in terms of potential energy distribution (PED), computed using a specially designed set of symmetry coordinates. The normal-mode analysis was described in detail and the PED matrix definition used in the calculations was provided. Particular attention has been devoted to the degenerate vibrations. The experimental infrared spectra of s-triazine and cyanuric acid isolated in low-temperature Ar matrices have been recorded and interpreted by comparison with the theoretically predicted normal modes. In the spectrum of matrix-isolated s-triazine, the IR bands originating from ¹³C and ¹⁵N isotopologues with one of the ring atoms substituted by a rare isotope were detected. These bands were identified thanks to the excellent agreement between the experimentally observed and theoretically predicted isotope shifts.     

Infrared spectrum and structure of the gold dihydroxide molecule

Reactions of laser-ablated gold atoms with H2O2 and H2+O2 mixtures give four new infrared absorptions, which match the four most intense vibrational frequencies calculated for Au(OH)2 using density functional theory; the calculations find a C2h structure and substantial covalent bonding character for the Au(OH)2 molecule, which is probably due to the high electron affinity of gold.     

Infrared spectrum of the CH3OCH2 radical in solid argon

The methoxymethyl radical, CH(3)OCH(2), is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH(3)OCH(3) in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm(-1), which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The O-CH(2) bond length is calculated to be 0.07 ? shorter than the CH(3)-O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH(3)OCH(2) radical to H(2)CO and CH(3) radical proposed for the gas phase process.     

A cyclic trimer of 2-(2-aminophenoxy)propionic acid with a bowl-shaped structure

A cyclic trimer of (R)-2-(2-aminophenoxy)propanoic acid, a δ-amino acid analogue, was synthesized. Molecular mechanics calculations on the cyclic trimer predicted that a concave network of sequential hydrogen bonds forms a C₃-symmetric bowl-shaped structure. Evidence for this conformation was found in the NMR spectra of the trimer in d-chloroform. Although the single-crystal structure of the cyclic trimer indicates that chloroform could be included in the bowl-shaped structure, the conformation was not C₃-symmetric and the hydrogen bonding network was of a different mode. These different conformations between solid and solution were reasonably clear from IR spectra.     

Infrared spectrum and structure of thorimine (HN=ThH2)

Laser-ablated thorium atoms react with ammonia to form thorimine (NH=ThH(2)), the first actinide imine to be reported. This work underscores the high reactivity of thorium atoms, particularly for N-H bond activation, reveals a new type of multiple bond to actinide atoms, and shows that this bond is strong for thorium as a result of an important contribution from the f orbitals.     

Infrared spectrum of several double oxides with corundum structure resulting from the transformation of lacunar γ phases with a spinel structure

When aluminum or chormium is substituted by Fe³⁺ ions in α-Fe₂O₃, all the ir bands gradually shift toward high frequencies. Alternatively, for the α phases of type (Fe₂Cr_4?yAl_y)O₉ the transition occurs sharply for a composition y close to 2. For α phases substituted by (Fe_6?yCr_y)O₉-type chromium a linear variation of frequency with chromium content is observed. From ir data it has been shown that, under given temperature and time conditions, an α phase less rich in chromium than the initial product could be obtained by oxidizing iron chromite. The ir spectrum of the oxidation of pure magnetites the size of which is between 1400 and 15000 Å evolves versus the latter to yield either the γ-Fe₂O₃ or the α-Fe₂O₃ phase which can be formed from γ-Fe₂O₃ or by direct oxidation of Fe₃O₄.     

Direct experimental observation of CS2OH.

The first experimental detection of CS(2)OH is reported. CS(2)OH was observed for about one microsecond after its formation, as an intact isolated species in the gas phase. It was generated by electron transfer to the CS(2)OH(+) ion, prepared in the source of a multisector mass spectrometer by suitable ion-molecule reactions. The vertical formation process allowed characterization of CS(2)OH by structural analysis of CS(2)OH(+). Theoretical calculations were performed at the B3LYP/6-311+G(2d,p) and CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2d,p) levels of theory. The computed structure and stability of CS(2)OH and CS(2)OH(+) as well as the energetics of the involved processes satisfactorily fit with the experimental results.     

A new molecular electronic emission spectrum observed in the reaction of F2 with CS2

A novel emission spectrum extending from 5500 to 8600 Å has been observed during the gas-phase reaction of F₂ with CS₂. Long progressions in the lower-state (presumably the ground-state) bending frequency and shorter progressions in a ground-state stretching frequency were observed. A partial vibrational analysis is reported, from which two new frequencies are obtained: v″₂ = 356 ± 5 and v″₃ = 8 31 ± 8 cm⁻¹ .The electronic origin lies near 18500 ± 1200 cm⁻¹. The spectrum is tentatively assigned to the FCS radical.