Equilibrium structure and vibrational frequencies of the O4 molecule

SCF closed shell calculations were performed to determine the equilibrium structure and vibrational frequencies of the O₄ molecule by means of Payne's method and with the help of the molecule's symmetry coordinates. The equilibrium geometry corresponds to symmetry group D_2d with R = 1.505 Å and h = 0.094 Å. The vibrational frequencies are: ν₅(E) = 885.5 cm^?1, ν₃(B₁) = 1051.9 cm^?1, ν₁(A₁) = 1018.3 cm^?1, ν₄(B₂) = 880.3 cm^?1. The second vibrational coordinate (A₁) corresponds to a double-well potential. The first vibrational levels were calculated by a variational method.     

Emission spectra of supersonically cooled dimethyldiacetylene cations

The ā²E_u → X?²E_g emission spectra of 2,4-hexadiyne (dimethyldiacetylene) cation and its d₃- and d₆-deuterated analogues were excited by electron impact on a seeded helium supersonic free jet. Vibrational analyses are made and vibrational frequencies in both states are inferred to ±1 cm^-1. Spin-orbit splittings are observed especially in degenerate overtone bands. The observed rotational contours allow a partial rotational analysis.     

Collisional relaxation Of HF(v = 3,4) By HF,CH4 and CD4

Direct excitation of overtone vibrations in combination with near-infrared fluorescence detection provides collisional relaxation rate constants for HF(v = 3,4) by HF, CH₄ and CD₄. Observing fluorescence from a few rotational levels shows that the rotational manifold in HF(v = 4) equilibrates in about half the gas kinetic collision time.     

A pure-dephasing model for overtone lineshapes

A model is developed for calculatinq the pure-dephasing (T₂) contribution to overtone lineshapes in isolated molecules. The linewidth is attributed to time-dependent fluctuations in the frequency of the overtone transition, resulting from the vibrational motions in the molecule, and no transfer of energy (intramolecular vibrational distribution) occurs in this picture. Numerical calculations for 2,3,5,6-paradeuterobenzene are presented.     

Experimental and theoretical study of the rovibrational relaxation of CH4 and CD4 by Ar

Experimental results are reported for the vibrational relaxation of the lowest bending modes of CH₄ and CD₄ br Ar in the temperature range of 140–376 K. Theoretical calculations are carried out in the framework of the semiclassical coupled-states approximation using asymptotic expressions of (3j) symbols and a first-order perturbation treatment. The confrontation of experimental and theoretical rate constants confirms the crucial role of rotational energy transfer upon the vibrational relaxation transfer.     

Vibrational relaxation in the group IVA trimethylmetal chlorides

The temperature dependence of the polarized and depolarized Raman spectra of the ν₂, ν₄, ν₆ and ν₇ modes were measured for t-butyl chloride and the analogous group IVA trimethylmetal chrlorides (silicon, germanium and tin). Analysis of the lineshapes revealed that isotropic second moments and vibrational relaxation times for a given mode remained approximately constant through the series. This tranferability of relaxation parameters between molecules extended to modulation times calculated from the Kubo formalism. The above results are in contrast to earlier studies on molecules of dissimilar structure. They provide some preliminary evidence that the mechanism of vibrational relaxation may be the same for equivalent modes in members of the series.     

Vibrational spectra and structure of dimethyl oxalate and dimethyl oxalate-d6

The vibrational spectra of dimethyl oxalate-d₆, have been examined in connection with a re-examination of the spectra and structure of dimethyl oxalate. The vibrational spectra of the compound had previously been interpreted as being consistent with a transC_2h structure in the solid phase and a non-planar C₂, form in the liquid and gas phases. This behaviour is not consistent with that observed in similar compounds and a re-evaluation of the facts suggests that the major spectral changes which are observed may be caused by destroying an intermolecular association in going from the solid to the liquid phase, which allows the methyl groups to assume positions out of the plane. Some modifications and additions have been made in the vibrational assignment and assignments are presented for the deuterated compound.     

Bandwidths in the gas phase overtone spectra of neopentane

The overtone spectrum of neopentane vapor is measured from 63 to 670 Torr. The bandwidth for δ_vCH = 5 is substantially smaller for the gas than the liquid. The local mode overtone bandwidths are much smaller than for other molecules. The results are discussed in terms of local mode coupling and vibrational state dynamics.     

Vibrational relaxation of ethylene oxide and ethylene oxide-rare-gas mixtures

The collision-induced vibrational energy relaxation of ethylene oxide (C₂H₄O) was studied by means of laser-induced fluorescence. The time-dependent population of the vibrational modes v₃ and v₅/v₁₂ was measured after excitation of CH-stretching vibrations near 3000 cm^?1. Rate constants for the vibrational energy transfer by collisions with C₂H₄O and the rare gases are deduced, and a simplified model for the vibrational relaxation of C₂H₄O is discussed.     

Infrared spectra of KNaSO4 and K3Na(SO4)2

The infrared spectra, transmittance and polarized reflectance, of KNaSO₄ and K₃Na(SO₄)₂ are reported. Group theoretical analysis was carried out and a vibrational assignment proposed on basis of C_3v and D_3d symmetries. Factor group and site effects are discussed.     

Comparison of CRDS to ICL-PAS and phase-shift CRDS spectroscopies for the absolute intensities of C–H (ΔvCH=6) overtone absorptions

Cavity ring-down spectroscopy (CRDS) has been used to obtain the visible overtone spectra (Δv_CH=6) of neo-pentane, C(CH₃)₄, propane, C₃H₈, and n-butane, C₄H₁₀, yielding absolute f-values for the transitions to better than 3%. For the neo-pentane overtone intensity, comparison with a recent measurement using intra-cavity laser photoacoustic spectroscopy (ICL-PAS) provides favourable agreement, with improved precision. Being absolute this value may be used as a standard for relative intensity measurements obtained by ICL-PAS. The measured propane and n-butane overtone intensities, when compared to recent work using phase-shift CRDS, indicate a lack of agreement to quoted uncertainties.     

The vibrational population inversion and relaxation kinetics of the C*2, d 3Πg state

The chemiluminescent spectra of C^*₂, d ³Π_g-a ³Π_u, Δ_v = O sequence from the reaction Na + CCl₄ have been obtained. The C^*₂, d ³Π_g,v' = 6 level is formed preferentially. The quenching and vibrational relaxation rates of the C^*₂, d ³Π_g state in Ar are 1.9 × 10⁶ and 2.2 × 10⁶ Torr^?1 s^?1, respectively. Na is one of the most efficient species for deactivation of C^*₂.     

Vibrational spectra and molecular symmetry of tetrasilylhydrazine and tetrasilylhydrazine-d12

The Raman spectra of tetrasilylhydrazine and tetrasilylhydrazine-d₁₂ have been recorded for the gas, liquid and solid phases from 25 to 2500 cm^?1. The infrared spectra of N₂(SiH₃)₄ and N₂(SiD₃)₄ have been recorded for the gas and solid phases from 40 to 2500 cm^?1. The vibrational data have been interpreted on the basis of a twisted (D_2d) molecular configuration for both the fluid and solid states.     

Vibrational spectroscopy of gaseous 1-methylcyclopentadiene and 2-methylcyclopentadiene

The infrared and fifth vibrational overtone (6v_CH) spectra of gaseous 1-methylcyclopentadiene and 2-methylcyclopentadiene are reported.     

Vibrational relaxation of N2(A3Σu+,υ = 1, 2,3) by CH4 and CF4

N₂(A, υ = 0-3) produced by the Ar(³P_0,2) + N₂ reaction and detected by laser-induced fluorescence undergoes rapid, stepwise vibrational relaxation but slow electronic quenching with added CH₄ or CF₄. Rate constants, k_Q^υ, of 1.5, 3.1, and 5.0 × 10^?12 cm³ s^?1 are measured for Q = CH₄, υ = 1-3, and 0.47, 1.8, and 5.5 × 10^?12 cm³ s^?1 for Q = CF₄, υ = 1-3, with ≈±20% accuracy (1σ). Information is also obtained for the unrelaxed, relative υ populations.     

D-isotope-labelled n-butane cations in CF3CCl3 and in CF2ClCFCl2: Structure and reactions at low temperature

Cations of n-butane, n-butane-1,4-d₆, -d₄, -d₂ and n-butane-2,3-d4 produced by X-irradiation of CF₂ClCFCl₂ and CF₃CCl₃ 3 matrices containing 1–2 mole% of solute have been investigated by ESR spectroscopy. The measurements have been performed at 77–130 K. The results confirm that the two largest couplings are assigned to two protons on the methyl groups. Smaller couplings have been resolved in CF₃CCl₃ and assigned to specific H atoms. A geometry with a non-planar carbon skeleton is proposed. Partly deuterated methyl groups give rise to rotational isomers. Thermal and photoinduced decompositions producing 2-butyl radicals and 2-butane cations have been further studied.     

Pulsed NMR study of NH4+ β-alumina

Proton NMR relaxation times T₂, T₁, and T_1? are reported for NH₄⁺ β-alumina powder in the temperature range 77 K < T < 500 K at 16 MHz. The measurements show that the NH₄⁺ ions both reorient and translate. The translational process can be characterized by the parameters E = 20 kJ mole^?1 and τ⁰_d = 3 × 10^?11 sec. Relaxation at high temperatures is dominated by dipolar coupling to paramagnetic impurities. Reasons for the different activation energies measured using NMR and other techniques for β-alumina compounds are discussed.     

The Raman spectra of ferrocene-b10 and -d10: librational modes and comments upon previous polarization data

The librational modes of ferrocene-h₁₀ and -d₁₀ have been observed near 62 cm^?1 (-h₁₀) and 40, 52 and 60 cm^?1 (-d₁₀). The polarization measurements at low temperatures can give no useful information concerning the vibrational assignment until the low temperature crystal structure is completely determined.     

Photoacoustic study of vibration to translation-rotation transfer inch4 and cd4

The vibrational deactivation of CH₄ and CD₄ is studied experimentally in the gas phase using the photoacoustic method. Excitations of v₄ and v₃ modes are performed. The corresponding kinetic models are established using the fact that vibration-to-vibrati transfers are very efficient and hold the adjacent vibrational levels in a quasi-equilibrium distribution. The models are tested between 140 and 376 K and the vibration to translation-rotation rate constants are determined in pure CH₄ pure CD₄, and CH₄-CD₄ mixtures.     

Mode-to-mode vibrational energy transfer in D2CO: Evidence of coriolis-enhanced rotational selectivity

Infrared—ultraviolet double resonance spectroscopy is used to demonstrate rapid collision-induced V-V transfer between the v₆ and v₄ vibrational manifolds of D₂CO. The rate of transfer is at least gas-kinetic and is explained in terms of Coriolis coupling and rotationally specific, quasi-resonant relaxation channels