High resolution emission Fourier transform infrared spectra of the 4p-5s and 5p-6s bands of ArH

In the 2500-8500 cm(-1) region several strong emission bands of (40)ArH were observed by Fourier transform spectroscopy through a dc glow discharge in a mixture of argon and hydrogen. Rotational-electronic transitions of the two previously unstudied 4p-5s and 5p-6s,v = 0-0, bands of (40)ArH were measured and assigned in the 6060 and 3770 cm(-1) regions, respectively. A simultaneous fit of the emission transitions of the 4p-5s and 5p-6s bands and an extended set of transitions of the 6s-4p band observed by Dabrowski, Tokaryk, and Watson [J. Mol. Spectrosc. 189, 95 (1998)] and remeasured in the present work yielded consistent values of the spectroscopic parameters of the electronic states under investigation. In the branch of the 4p-5s band with transitions of type (Q)Q(f(3)e) we observed a narrowing in the linewidths with increasing rotational quantum number N. The rotational dependence of the linewidth is caused by predissociation of the 5s state by the repulsive ground 4s state through homogeneous coupling and changes in overlap integrals of the vibrational wave functions with the rotational level. Analysis was based on the Fermi's golden rule approximation model. In the 4p-5s band region a vibrational sequence ofv(')-v(")=1-1, 2-2, and 3-3 were recorded and a number of transitions belonging to the strongest (Q)Q(f(3)e) form branch of the 1-1 band were analyzed.     

High resolution infrared spectra of H2-Kr and D2-Kr van der Waals complexes

Infrared spectra of weakly bound hydrogen-krypton complexes have been studied at high spectral resolution (0.04 cm(-1)) using a long-path (154 m) low temperature (100 K) absorption cell and a Fourier transform spectrometer. In addition to spectra from the regions of the H(2) and D(2) fundamental vibrational bands in the midinfrared, the results also include the region of the pure rotational S(0)(0) transition of H(2) in the far infrared. A total of 219 measured line positions from these spectra have been fully assigned to specific quantum transitions and form the basis for determining a greatly improved semiempirical three-dimensional intermolecular potential energy surface for hydrogen-krypton in an accompanying paper.     

Abnormal inversion splitting in NH2D: rotational analysis of the nu5 bending vibrational band system

A high-resolution Fourier transform infrared spectrum of the nu(5) bending vibrational band system region of the partially deuterated ammonia molecule NH(2)D has been measured and rotationally analyzed. The spectrum consists of strong a-type transitions between the states of same vibrational symmetry and weaker c-type transitions between the states of different vibrational symmetry. The Hamiltonian model used includes interaction terms between the rotational states of both upper and lower inversion doublets. The vibrational term values for the symmetric and the antisymmetric component of the upper-inversion doublet are 1,605.637 965(620) cm(-1) and 1,590.993 82(100) cm(-1), respectively, where the numbers in parentheses are one-standard deviations in the least significant digit. These figures are close to the corresponding values 1,605.62 cm(-1) and 1,590.72 cm(-1) obtained recently from results based on high-level ab initio calculations. The order of the vibrational term values is abnormal in the ammonia family, as typically the symmetric state is lower in wavenumber than the antisymmetric one.     

High resolution spectra and conformational analysis of 2-butoxy radical

We have recorded five high resolution (200 MHz), rotationally resolved, vibrational bands of the B-X electronic transition of 2-butoxy. Two bands of the 2-butoxy spectrum have been rotationally analyzed and assigned to two different geometrical conformers of the molecule. The analyses allow the determination of the six experimental rotational constants defined by the geometry of the species in the ground (X) and excited (B) electronic states and also four spin-rotation constants for the X electronic state of the conformers. Comparison of the experimental rotational constants with the results of ab initio computations provides unambiguous conformational assignment of these bands. This approach can be extended to assign two other spectral bands to the third 2-butoxy conformer.     

High-resolution infrared study of vinyl fluoride in the 750-1050 cm(-1) region: rovibrational analysis and resonances involving the nu8, nu10, and nu11 fundamentals

The FTIR spectra of CH2[double bond]CHF have been investigated in the nu(8), nu(10), and nu(11) region between 750 and 1050 cm(-1) at a resolution of about 0.002 cm(-1). The nu(8) vibration of symmetry species A' gives rise to an a/b-type hybrid band, while the nu(10) and nu(11) modes of A' ' symmetry produce c-type absorptions. Due to the proximity of their band origins, the three vibrations perturb each other by Coriolis and high-order anharmonic resonances. In particular, the interactions between the nu(8) and nu(10) modes are very strong and widespread with band origins separated by only 1.37 cm(-1). Besides the expected c-type characteristics, the nu(10) band shows a very intense pseudo a-type component caused by the strong first-order Coriolis resonances with the nu(8) state. Furthermore, the 2nu(9) "dark state" was found to be involved in the interacting band systems. The spectral analysis resulted in the identification of 3144, 3235, and 3577 transitions of the nu(8), nu(10), and nu(11) vibrations, respectively. Almost all the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the Ir representation and the perturbation operators. The model employed includes nine types of resonances within the tetrad nu(8)/nu(10)/nu(11)/2nu(9) and a set of spectroscopic constants for the nu(8), nu(10), and nu(11) fundamentals as well as parameters for the "dark state" 2nu(9), and fourteen coupling terms have been determined.     

Observation and rovibrational analysis of the intermolecular NH3 libration band nu9(1) of H3N-HCN

The high-resolution far-infrared absorption spectrum of the gaseous molecular complex H(3)N-HCN is recorded by means of static gas-phase Fourier transform far-infrared spectroscopy at 247 K, using a synchrotron radiation source. The spectrum contains distinct rotational structures which are assigned to the intermolecular NH(3) libration band nu9(1) (nu(B)) of the pyramidal H(3)N-HCN complex. A rovibrational analysis based on a standard semirigid symmetric top molecule model yields the band origin of 260.03(10) cm(-1), together with values for the upper state rotational constant B' and the upper state quartic centrifugal distortion constants D'(J) and D'(JK). The values for the upper state spectroscopic constants indicate that the hydrogen bond in the H(3)N-HCN complex is destabilized by 5% and elongates by 0.010 A upon excitation of a quantum of libration of the hydrogen bond acceptor molecule.     

Spectrum and dynamics of the CH chromophore in CD2HF. I. Vibrational Hamiltonian and analysis of rovibrational spectra

We have measured the complete rovibrational spectrum of dideutero-fluoro-methane (CD₂HF) from the far-infrared (20 cm⁻¹) to the visible (14000 cm⁻¹) largely at Doppler-limited resolution. Rovibrational parameters are reported for CH-stretching and bending fundamentals and overtones. The spectra of the coupled stretching and bending modes of the CH chromophore are analyzed quantitatively both in terms of effective Hamiltonians and a three-dimensional model Hamiltonian. A new numerical method for solving the corresponding eigenvalue problem is described briefly. The strong Fermi and Darling—Dennison resonances lead to fast vibrational redistribution on the femtosecond time scale.     

Combined analysis of microwave and infrared spectra of methyl iodide: rotational and l-type doubling constants of the v5, v3+v6 and v2 states

The rotational constant B and the l-type doubling constant q were determined for the v₅, v₃+v₆ and v₂, states of CH₂I from the microwave transition frequencies, in combination with the infrared data previously reported. Since these vibrational states were coupled through the Fermi resonance and the xy-type E-E and A₁-E Coriolis resonances, the analysis was made by setting up and solving the complete form of the secular determinants of the energy matrices. The rotational and l-type doubling constants were determined as B₅, = 0.250 173 cm^?1, B₃₆ = 0.247 600 cm^?1, B₂ = 0.249 369 cm^?1, q₅ = ?0.000 027 cm^?1 and q₃₆ = ?0.000 179 cm^?1, which are unperturbed by Fermi and Coriolis interactions. Other band constants for v₅ and v₃+v₆ were also refined in accordance with the new values of B₅ and B₃₆. The present study indicated that the combined analysis of microwave and infrared spectral data was useful for the precise determination of vibration-rotation, levels in the perturbed system.     

ClClO2 is the most stable isomer of Cl2O2. Accurate coupled cluster energetics and electronic spectra of Cl2O2 isomers

High level ab initio electronic structure calculations at the coupled cluster level with a correction for triples (CCSD(T)) extrapolated to the complete basis set limit have been made for the thermodynamics of the Cl2O2 isomers: ClClO2, ClOOCl, and ClOClO. The ClClO2 isomer is predicted to be the most stable isomer and is more stable than ClOOCl by 3.1 kcal/mol at 298 K. The ClOClO isomer is less stable than ClOOCl by 8.3 kcal/mol at 298 K. The weakest bond in ClClO2 is the Cl-Cl bond with a bond dissociation energy (BDE) of 24.4 kcal/mol, and the smallest BDE in ClOOCl is the O-O bond with a value of 18.0 kcal/mol. The smallest BDE in ClOClO is for the central O-Cl bond with a BDE of 9.7 kcal/mol. Electronic transitions were calculated with the equations of motion EOM-CCSD method. The calculations clearly demonstrate that singlet states of ClClO2 absorb to longer wavelengths in the visible than do the singlet states of ClOOCl as does ClOClO.     

La2O3-Mo5Si3/MoSi2复合材料的高温氧化行为

研究了0．8％La2O3-MosSi3／MoSi2复合材料在1200℃空气中的高温氧化行为。结果表明：0．8％稀土和MoSi3的加入，使材料的抗氧化性能降低。MosSi3含量越高，材料的抗氧化性能越差。当MosSi3含量低于30％时，在氧化初始阶段，质量变化呈直线下降，随着氧化的进行，氧化逐渐增重，材料表面形成较致密的SiO2阻止了材料的进一步氧化，使得氧化增重较小。而0．8％La2O3-40％Mo5Si3／MoSi2复合材料却出现了“粉化”现象。0．8％La2O3．MosSi3／MoSi2复合材料抗氧化性能的降低，归因于Mo5Si3差的抗氧化性和材料致密度的降低；另外，稀土和Mo5Si3的加入，细化了材料的晶粒，使晶界面积增加，加速了氧在晶界中的扩散，促进了材料的氧化。     

Characterization of silicon-carbon clusters by infrared laser spectroscopy: the nu 3(sigma u) band of linear Si2C3

The nu 3(sigma u) fundamental vibration of 1 sigma g+ Si2C3 has been observed using a laser vaporization-supersonic cluster beam-diode laser spectrometer. Forty rovibrational transitions were measured in the range of 1965.8 to 1970.9 cm-1 with a rotational temperature of 10-15 K. A least-squares fit of these transitions yielded the following molecular constants: nu 3(sigma u)=1968.188 31(18) cm-1, B"=0.031 575 1(60) cm-1, and B'=0.031 437 4(57) cm-1. These results are in excellent agreement with recent Fourier transform infrared (FTIR) measurements of Si2C3 trapped in a solid Ar matrix [J. Chem. Phys. 100, 181(1994)] and with ab initio calculations [J. Chem. Phys. 100, 175 (1994)] which suggest cumulenic-like bonding for Si2C3, analogous to the isovalent C5 carbon cluster.     

Fourier transform-based deconvolution techniques for resolution of overlapping bands in x-ray photoelectron and fourier-transform infrared spectra of bisphenol-a-polycarbonate/dimethyl siloxane block copolymers

A series of bisphenol-A-polycarbonate/poly(dimethylsiloxane) (BPAC/DMS) block copolymers is studied by x-ray photoelectron (x.p.s.) and Fourier-transform infrared (F.t.i.r.) spectroscopies. Previous quantitative results, obtained without resolution enhancement, provided calibration of the signal-processing techniques used. A Van Cittert technique for x.p.s. is evaluated for the deconvolution of the carbon 1s core photoelectron spectrum, and self-deconvolution by Fourier methods is evaluated for the overlapping Si-CH₃ and aromatic C—O stretch bands at 1261 and 1228 cm^-1, respectively, in the i.r. spectrum. These features can be utilized in quantitative analysis of the surface and bulk of the BPAC/DMS copolymers. The ability of deconvolution techniques to narrow the bands artificially so as to resolve complex spectral envelopes, while retaining the quantitative data is discussed. The studies illustrate the ability of modern signal processing techniques to extract exact complex data from spectroscopic results, and allow quantitative evaluation without standards for complex polymer systems.     

Vibrational spectra and structure of CH3Cl:H2O, CH3Cl:HDO, and CH3Cl:D2O complexes. IR matrix isolation and ab initio calculations

The infrared spectra of CH3Cl + H2O isolated in solid neon at low temperatures have been investigated. The CH3Cl + H2O system is remarkable because of its propensity to form CH3Cl:H2O and CH3Cl:(H2O)n (n > or = 2) complexes. We focus here on the CH3Cl:H2O species. Low concentration studies (0.01-0.5%) and subsequent annealing lead to formation of the 1:1 CH3Cl:H2O complex with O-H. . .Cl-C or O. . .H-C intermolecular hydrogen bonds. Vibrational modes of this complex have been detected. In addition, spectra of D2O + CH3Cl and HDO + CH3Cl have also been recorded. A detailed vibrational analysis of partially deuterated species shows that HDO is exclusively D bonded to CH3Cl. This is a consequence of the preference for HDO to form a deuterium bonding complex rather than a hydrogen bonding one.     

Absorption spectra of SiCl4, Si2Cl6, SiF3CH3 and GeF4 in the VUV region

In the range 110–200 nm the absorption features of Si₂Cl₆ closely resemble those of SiCl₄ and the peaks observed are tentatively assigned to the Rydberg transitions of a Cl lone-pair electron. Two diffuse bands in the SiF₃CH₃ absorption are also assigned to Rydberg excitations. The spectrum of GeF₄ shows a broad band considered to be a valence excitation of the outermost orbital. The emission of the SiCl₂ (ùB₁→X̃¹A₁) transition was found in the photoexcitation of Si₂Cl₆.     

Lifetime measurements of the 3D3/2 and 3D5/2 metastable states in CaII

The lifetime of the metastable 3D_3/2 and 3D_5/2 states of Ca⁺ ions is determined in a r.f. ion trap by laser excitation of this levels and subsequent time delayed probing of the state population by a second laser. In a buffer gas atmosphere of about 10^–5–10^–6 mbar of He we observe quenching to the ground state and strong finestructure mixing of the two D-states. This mixing allowes only the determination of the combined lifetime. Our result of (3D)=1.24(39) s is in good agreement with theoretical calculations.     

Unimolecular rate constants for HX or DX elimination (X = F, Cl) from chemically activated CF3CH2CH2Cl, C2H5CH2Cl, and C2D5CH2Cl: threshold energies for HF and HCl elimination

Vibrationally activated CF(3)CH(2)CH(2)Cl molecules were prepared with 94 kcal mol(-1) of vibrational energy by the combination of CF(3)CH(2) and CH(2)Cl radicals and with 101 kcal mol(-1) of energy by the combination of CF(3) and CH(2)CH(2)Cl radicals at room temperature. The unimolecular rate constants for elimination of HCl from CF(3)CH(2)CH(2)Cl were 1.2 x 10(7) and 0.24 x 10(7) s(-1) with 101 and 94 kcal mol(-1), respectively. The product branching ratio, k(HCl)/k(HF), was 80 +/- 25. Activated CH(3)CH(2)CH(2)Cl and CD(3)CD(2)CH(2)Cl molecules with 90 kcal mol(-1) of energy were prepared by recombination of C(2)H(5) (or C(2)D(5)) radicals with CH(2)Cl radicals. The unimolecular rate constant for HCl elimination was 8.7 x 10(7) s(-1), and the kinetic isotope effect was 4.0. Unified transition-state models obtained from density-functional theory calculations, with treatment of torsions as hindered internal rotors for the molecules and the transition states, were employed in the calculation of the RRKM rate constants for CF(3)CH(2)CH(2)Cl and CH(3)CH(2)CH(2)Cl. Fitting the calculated rate constants from RRKM theory to the experimental values provided threshold energies, E(0), of 58 and 71 kcal mol(-1) for the elimination of HCl or HF, respectively, from CF(3)CH(2)CH(2)Cl and 54 kcal mol(-1) for HCl elimination from CH(3)CH(2)CH(2)Cl. Using the hindered-rotor model, threshold energies for HF elimination also were reassigned from previously published chemical activation data for CF(3)CH(2)CH(3,) CF(3)CH(2)CF(3), CH(3)CH(2)CH(2)F, CH(3)CHFCH(3), and CH(3)CF(2)CH(3). In an appendix, the method used to assign threshold energies was tested and verified using the combined thermal and chemical activation data for C(2)H(5)Cl, C(2)H(5)F, and CH(3)CF(3).     

Experimental and theoretical study of line mixing in NH3 spectra. II. Effect of the perturber in infrared parallel bands

In a previous paper [J. Chem. Phys. 116, 7544 (2002) (Paper I)] a model, based on the energy corrected sudden approximation, was proposed for the construction of the line-mixing relaxation matrix. It was successfully tested by comparisons with measured infrared spectra of ammonia-helium mixtures. The present paper extends this preliminary study by considering mixtures of NH3 with H2 and Ar. Measurements have been made at room temperature in the regions of the nu2 and nu1 bands for pressures up to several hundred atmospheres. As in Paper I, the relaxation operator is constructed, within the impact approximation, using the ECS approximation. The data required are dynamical factors (which can be predicted from the NH3-X potential energy surface) and a scaling length (adjusted using line broadening data). Comparisons between measured and calculated absorptions demonstrate the quality of the model which satisfactory corrects for the large deviations with respect to the purely Lorentzian behavior. Line-mixing effects for NH3-Ar and NH3-H2 are qualitatively similar to those observed for NH3-He but quantitative differences exist, particularly when intra- and interbranch couplings are considered. Finally, the proposed model leads to very satisfactory results in the wings of both the purely rotational and nu2 bands of NH3 diluted in H2, opening promising perspectives for the remote sensing study of planetary atmospheres.