K-shell excitation of CH4, NH3, H2O,CH3OH,CH3OCH3 and CH3NH2 by 2.5 keV electron impact

The regions around the respective carbon, nitrogen and oxygen K-edges of CH₄, NH₃, H₂O, CH₃OH, CH₃OCH₃ and CH₃NH₂ have been investigated by electron energy loss spectroscopy using a beam of 2.5 keV electrons. All spectra show a number of discrete peaks just below the K-shell ionization threshold. These discrete structures have been interpreted as being associated with the promotion of a K-shell electron to Rydberg orbitals which converge to the K-shell ionization threshold.     

Relation between electrooptical constants and polar tensors of CH3F,CD3F,CH3Cl,CD3Cl,CH3Br,CD3Br,CD3I,and CD3I

Infrared intensity analysis was done in two ways. In one approach, formulas connecting electrooptical parameters (eop's) and intensities were derived and, using the intensities, the former were obtained. In evaluating the eop's the intensity sum equations were used directly so that the sign ambiguity of $\text{δP}\text{δQ}$ is avoided. In the other method, polar tensors were obtained directly from intensities. The two methods have now been connected, and polar tensors have been obtained in terms of electrooptical parameters so that the former were also free from sign ambiguity of $\text{δP}\text{δQ}$. They compare well with those obtained directly from intensities. In similar connecting formulas by other authors [see, for example, P. L. Prasad, J. Chem. Phys., 69, 4403, (1978)], both polar tensors and eop's were affected by the sign ambiguity.     

Absolute Raman intensities of CH4, CH3D,CH2D2, CHD3, and CD4

Measurements of the absolute vibrational Raman intensities and depolarization ratios for the fundamental and some overtone and combination bands of CH₄, CH₃D, CH₂D₂, CHD₃, and CD₄ are reported. Experimental aspects of these measurements are discussed. The experimental data conform satisfactorily to all isotope intensity sum rules. The measured intensities and depolarization ratios, together with the vibrational potential function for CH₄, make possible the calculation of the four independent parameters of the isotopic invariant quantities $\text{α}{}^{\mathrm{S}}\text{= |}\text{?α}\text{?S}\text{|}$. The results deduced from these agree with all 36 experimentally observed values. Values of electro-optical parameters for the CH bond are calculated and discussed.     

交叉分子束方法研究H+CH4和H+CD4反应:CH3/CD3的振动激发态产物通道

We study the H+CH₄/CD₄→H₂/HD+CH₃/CD₃ reactions using the time sliced velocity map ion imaging technique. Ion images of the CH₃/CD₃ products were measured by the (2+1) resonance enhanced multi-photon ionization (REMPI) detection method. Besides the CH₃/CD₃ products in the ground state, ion images of the vibrationally excited CH₃/CD₃ products were also observed at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of the products CH₃/CD₃ in vibrationally excited states gradually vary from backward scattering to sideways scattering as the collision energy increases. Compared to the CH₃/CD₃ products in the ground state, the CH₃/CD₃ products in vibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a more important role in the vibrationally excited product channels.     

Microwave spectra of dimethylsulfide-d6, (CD3)2S,ground and excited torsional states

The microwave spectra of the molecular isotope (CD₃)₂S in the ground state and the first and second excited states of methyl top torsion (internal rotation) and of CSC deformation as well as the ground-state spectra of the ¹³C and ³⁴S substituted forms have been measured. The rotational constants and centrifugal distortion and rotation-vibration interaction constants could be determined. The rotational lines in the excited torsional states (1₁, 1₂, 2₁, 2₂, 2₃) were found to be split into quartets due to the interaction between molecular rotation and methyl top internal rotation. The experimental multiplet splittings were fitted to those calculated from a rotation-internal rotation Hamiltonian in order to obtain values for the internal rotation barrier V₃ and the top-top interaction potential coefficients V₁₂ and V′₁₂. V₁₂ was too highly correlated with V₃ for a separate determination. The values following from the least-squares adjustment are discussed.     

Low temperature far IR spectra of (CH34)N NiCl3, (CH3)4N NiBr3 and (CD3)4N NiBr3

The known phase transition in (CH₃)₄N NiCl₃, at 171 K, has been characterised by far IR spectroscopy. The transition is explained as due to a formation of weak labile C-H,…, Cl hydrogen bonds at low temperatures, restricting the “free” internal rotations of the methyl groups and perhaps at the same time ordering the orientations of the tetramethylammonium ions. No similar transition in (CH₃)₄N NiBr₃ was found.     

Infrared spectra of 1-phosphapropyne,CH3CP,and its perdeuteride,CD3CP

The infrared spectra of 1-phosphapropyne, CH₃CP, and its perdeuteride, CD₃CP, have been measured in the gaseous and solid states. The Q_K branches of perpendicular bands have been analyzed in terms of the usual quadratic expression in K. Fermi resonances were identified for the ν₁, ν₂ + ν₃, 2ν₃, 2ν₆⁰; and ν₅, 2ν₃ + ν₈ band systems of CH₃CP and the ν₁, 2ν₃, 2ν₆⁰; ν₆, ν₇ + ν₈; and ν₇, 3ν₈¹ band systems of CD₃CP. The xy Coriolis interaction was also identified between the ν₃ and ν₆ bands of the two species. All the fundamentals were assigned and the normal coordinate treatment was carried out along with the Coriolis constants, ζ^z.     

PAM analysis of the microwave spectra of thioacetic acid,CH3COSH and CH3COSD

The microwave spectra of two isotopic species of thioacetic acid, CH₃COSH and CH₃COSD, have been studied. Using the principal axis method (PAM), including terms through n = 6 in the perturbation series and the denominator correction, the spectra were analyzed and 45 lines for CH₃COSH and 40 lines for CH₃COSD were assigned. The parameters obtained by the least-squares analysis are A = 9913.29 ± 0.56 MHz, B = 4923.11 ± 0.23 MHz, C = 3354.60 ± 0.24 MHz, θ = 57.080 ± 0.030°, s = 6.2980 ± 0.0012, and I_α = 3.198 ± 0.020 amu$\text{A}\text{?}{}^2$ for CH₃COSH, and A = 9662.80 ± 0.78 MHz, B = 4810.74 ± 0.26 MHz, C = 3273.92 ± 0.18 MHz, θ = 55.097 ± 0.024°, s = 5.9742 ± 0.0016, and I_α = 3.171 ± 0.020 amu$\text{A}\text{?}{}^2$ for CH₃COSD. The barrier to internal rotation of the methyl group is V₃ = 222.6 ± 1.4 cal/mole for CH₃COSH and V₃ = 212.9 ± 1.4 cal/mole for CH₃COSD. The Stark effect measurements of A species transitions for CH₃COSH led to the dipole moment μ = 1.821 ± 0.013 D with the components μ_a = 0.191 ± 0.010 D and μ_b = 1.811 ± 0.013 D.     

Thermal expansion of solid CH4 and CD4

The linear expansion coefficients of solid light methane CH₄ and deuteromethane CD₄ have been denned in the temperature range 10°–24°K and 6°–58°K, respectively. The question about the nature of rotational motion of molecules in CH₄ and CD₄ crystals and about the existence of low temperature phase transition in solid methane is discussed.     

The microwave spectra of ortho-fluorotoluene with the asymmetric internal rotors CH2D and CD2H

The rotational spectra of αd₁- and αd₂-ortho-fluorotoluene in the ground state of the methyl group torsion have been measured. The evaluation of the spectra has been based on the theory for the internal rotation of an asymmetric internal top formulated earlier by several authors. The barrier potential being threefold symmetric (V₃), each torsional level consists of three nondegenerate substates, designated as sy and ±asy. The sy-state is assigned to the conformation with the unique methyl hydrogen isotope within the molecular heavy-atom plane (sy-rotamer), while the ±asy-states belong to the respective out-of-plane conformation (asy-rotamer). In the torsional ground state the level spacing between the ±asy substates is very small and numerous accidental close degeneracies are present between the rotational level systems based on these torsional substates. The rotational levels involved are strongly perturbed by the coupling between molecular overall rotation and internal rotation. Large deviations from a rigid rotor spectrum and (+) ? (?) intersystem (“tunneling”) transitions are observed. The spectrum of the asy-rotamer can be well reproduced by a “two-dimensional” Hamiltonian containing 11 “rotational constants,” 9 of which are determined by a fit to the spectrum. Several are sufficiently barrier-dependent to derive V₃. We obtain (in cal/mole) 567 ± 48 for αd₁-ortho-fluorotoluene, 711 ± 40 for the αd₂-isotope. The deviations from 649 cal/mole for the normal isotope are appreciable, probably indicating shortcomings of the semirigid model. The sy-rotamer presents a rigid rotor spectrum.     

Vibrational spectra of (CD3)2Cd and (CD3)2Zn

The Raman and infrared spectra of (CH₃)₂Cd and (CH₃)₂Zn have been reexamined and are reported along with previously unreported vibrational data for (CD₃)₂Cd and (CD₃)₃Zn. The spectra have been analyzed using the double group $\text{G}{}_{36}\text{2}$, which has led to some changes in assignments made previously. Comparison is also made with a recent study of (CH₃)₂Hg and (CD₃)₂Hg. Fine structure was observed for two of the vibrations of the E_1d symmetry species, arising from internal rotation of the methyl groups. This structure has been analyzed using a recently developed theory for molecules of the freely rotating dimethylacetylene type. Problems which arise in the application of this theory have been pointed out, and it is suggested that some additional consideration of the theory may be necessary.     

Pionic x-ray intensities from C,CH2 and CD2

The relative intensities of the carbon L_α and L_β pionic X-ray lines from graphite, polythylene, and deuterated polyethylene have been measured. No differences between CH₂ and CD₂ were observed, but differences were found between graphite and the two polyethylene targets.     

Vibration-rotation spectra of CD3CCH

Rotational structure in the perpendicular fundamentals ν₆, ν₇, and ν₈, and in the parallel component of 2ν₉ of CD₃CCH are fully analyzed at a resolution of 0.2–0.3 cm^?1. The A₁-E Coriolis resonances between ν₄ and ν₇, and ν₅ and ν₈ are analyzed by computer contour simulations. These permit accurate location of the parallel fundamentals, and determination of the associated Coriolis interaction constants. The fundamental vibrations ν₅ and ν₈ in CD₃CCH lie only 4 cm^?1 apart, and constitute the closest accidental Coriolis resonance yet studied by the simulation technique. The force field of methyl acetylene, constrained according to the hybrid orbital model, is calculated, using the recently determined molecular structure, and fitting all observed data, many of which have been revised in a number of recent studies.     

Force field variations along the torsional coordinates of CH3OH and CH3CHO

We examine the question of reduced Hamiltonians for the torsion-rotation problem and in particular the question of the continuity of frequencies obtained by projecting out a large-amplitude torsional coordinate. We find that suitable results for torsion-rotation analysis can be obtained using either a rectilinear or a curvilinear formalism.     

Far-infrared internal rotation spectrum of CH3OD and CD3OD

The far-infrared spectra of the Q branches of hindered rotation in CH₃OD and CD₃OD have been investigated in the 80- to 250-cm^?1 spectral region. The theoretical spectra are calculated using the full set of Kirtman constants and are compared with the experimental spectra of resolutions up to 0.13 cm^?1.     

Microwave spectra of CD3OH methanol

The microwave spectrum of CD₃OH has been studied over the 8 to 58 GHz region, and numerousb-type transitions have been assigned. Many of these belong toP subbranches which descend to the microwave region from subband origins lying much higher in the far-infrared, pass through zero frequency, and return upward again. Others are members ofb-typeQ branches which extend across the region. As well, variousa-typeK-doublet lines arising as transitions directly across the split levels of asymmetry doublets have been identified.     

Microwave spectra of CH314NC and CH315NC in the 3ν8 state

The microwave spectra of methyl isocyanide and its ¹⁵N derivative in the 3ν₈ state have been observed from 40 to 180 GHz. After the assignment by a graphical method, the analysis has been carried out, first by the reuse of analytical formulas and then by the diagonalization of the energy matrix. Many accidental resonances have been shown to occur between the l = ±1 states, and A₁A₂ doublings for K, l = ±3, ±3 have been discovered. A set of constants in the 3ν₈ state is given for each molecule.     

A study on the GVFF of CHF3, CH2F2, and CH3F

The complete GVFF of CHF₃, CH₂F₂, and CH₃F has been calculated from self-consistent-field ab initio energies, using a 4–31 G basis set. The larger part of the interaction force constants is close to those of the best available force fields from experimental data. Only one interaction term in CH₃F and the interaction force constants of the A₁ species in CH₂F₂ differ appreciably from the experimental ones. Using constraints from the ab initio studies we have improved the GVFF of CH₃F and CH₂F₂. It is shown that all comparable stretch-stretch interaction terms are of the same order of magnitude in the three molecules. The sign of all stretch/bend force constants are in accordance with those predicted by the hybrid orbital force field.     

The microwave spectra and vibration-rotation interaction constants for CD3I in the excited vibrational states

The microwave spectra in the J = 1 → 3 region for CD₃I has been observed and six excited vibrational states assigned. The vibration rotation interaction constants, α^B and nuclear quadrupole coupling constants, eQq, have been determined for the states: ν₂, ν₃, ν₅, ν₆, 2ν₃, and ν₃ + ν₆. For the degenerate vibrational states, the l type doubling constants, q_t were determined.     

P-branch operation of CD3F and CH3F Raman FIR lasers

Multi-kolowatt pulses with limited wavelength tunability have been produced in several bands between 186 and 817 m by pumping v3 P-branch transitions in¹²CH₃F and¹²CD₃F with the 10.6 m band of a ten-atmosphere CO₂ laser. The FIR emissions are all restricted to the immediate neighborhood of the resonances associated with successive J-numbers, but there is some evidence that additional off-resonant emission could be produced with stronger pumping. The optimum operating pressure for the various molecule/J-number combinations range from 7 to 75 torr and increase rapidly with increasing J-number.