A study of the line width in the rotational spectrum of methylfluoride

The results of a study on the line width in the pure rotational spectrum of methylfluoride are presented. The experimental values of the normalized line width as a function of the line number show a maximum at m = 16. There is good qualitative agreement with the theoretical results obtained with the quantum mechanical theory of Murphy and Boggs, although there remains a discrepancy in absolute value. An important result is that the Murphy and Boggs theory predicts quite accurately the temperature dependence of the line width.     

New approach to single-particle time-correlation function theory: Application to intramolecular dephasing in the condensed phase

A new approach to solve the linewidth expression of infrared line shape based on the Kim-Wilson single-particle time-correlation function theory is presented. A projection-operator technique coupled with an explicit series-expansion method is used to reduce the unusual operator exp[1(1 - P)Lt] in the damping function to the usual operator exp(i L⁰t). This approach is applied to a study of a temperature dependence of the width and shift of the infrared line shape for intramolecular dephasing of a polyatomic molecule in the condensed phase.     

Angular dependent linewidths of ESR spin probes in oriented smectic systems. An application to oriented lecithin—cholesterol multibilayers

A theory, based on the diffusion model of molecular reorientation extended with an orienting potential, is developed for the angular dependence of the ESR linewidths of symmetrical top radicals in oriented smectic liquid crystals. The theoretical results have been compared with linewidth data obtained with the cholestane spin label in oriented multibilayers of equimolar quantities of dipalmitoyl lecithin and cholesterol. For the determiination of the linewidths, the ESR spectra were fitted to a line shape function, which includes unresolved proton hyperfine interactions.From the comparison of theory and experiment the rotational diffusion tensor and order parameter S can be found, giving D_⊥ = 3.4 × 10⁶ s^?1, D|/D_⊥ = 40 and S = 0.86 at 49°C. The high value of D|/D_⊥ indicates a strong anisotropic motion of the cholestane spin label. The order parameter found is in good agreement with the order parameter calculated from the angular dependence of the ESR line positions.     

Electron impact induced Balmer line emission from some aliphatic hydrocarbons

Absolute Balmer line emission cross sections are determined. The Balmer emission is obtained by dissociative electron excitation in propane, propylene and n-butane. The optical excitation functions measured for these lines are investigated in the medium energy range of 50–700 eV and normalized by a He bench-mark procedure. The measured data are corrected by an apparatus collection efficiency factor F to compensate for the loss of optical signal due to non-thermal energies of H-excited molecular fragments. The obtained results are determined with an accuracy of ± 15%. The absolute Balmer line cross sections are analysed according to the Bethe theory to get some information on primary excited parent molecular states. The power-law dependence for Balmer series has been determined.     

Viscosity of random coil polymers with nonzero thickness

The concentration dependence of the shear viscosity of a suspension of cylinders with random flight axes is studied at low concentrations. The intrinsic viscosity and the Huggins coefficient are found to depend on the radius, a, of the cylinder only as a series expansion in powers as a²/IL (I is the Kuhn step length and L is the contour length of the cylinder axis). The leading terms give identical results to those of Freed—Edwards theory; the zero concentration limit of the leading term reproduces the Kirkwood—Riseman result for a random flight line distribution of friction.     

Electron exchange in the tetracyanoquinodimethane system: Unexpected dependence on solvent polarity and viscosity

The electron transfer rate between tetracyanoquinodimethane and its radical anion is measured for different solvents and temperatures using ESR line broadening. The solvent polarity term γ = 1/n² - 1/ε (n is the refractive index, ε the dielectric constant) could be changed in the range 0.05 ≤ γ ≤ 0.53. The true rate constants k (corrected for diffusion) are discussud in terms of the classical theory of electron transfer. A linear dependence of ln k on γ is only found with a viscosity-dependent pre-exponential factor. The outer reorganization energy is small compared with the inner and has a negative sign. This is explained by the special arrangement of the ellipsoidal reactants in the activated complex.     

Viscosity dependence of internal conversion rates of polyatomic molecules

A microscopic theory of the dependence of internal conversion rates (R) on viscosity (η) is developed by extending usual theories of vibronic energy relaxation. The viscosity dependence of R is assumed to arise from the viscosity dependence of the damping rates γ of soft (torsional) modes of intramolecular vibration (frequencies ω). From the theory developed R is found to increase with η when γ « ω. When γ ? ω the rate R is found to decrease with η. In this case the dependence of R on η can often be approximated in a wide range of η according to R ∝ η^?α. The value of α depends on certain microscopic parameters, and 0 ? α ? 1 and α ? 1 might be found. In particular, the Oster-Nishijima result (α = 1) is included as a limiting case. A comparison between theory and experiment is given, which shows the theoretical results to be in full agreement with the experimental ones.     

Influence of RF power and nebulizer type on the intensity of the important cadmium lines in ICP spectroscopy

The authors studied the dependence of the net line intensity (x) on RF power (P) for three Cd lines with two different nebulizers a pneumatic and an ultrasonic nebulizer. The dependence of x on P was found to be different for the two nebulizer types and this difference is attributed to a difference in droplet size and a consequent difference in the rate of water introduction into the plasma associated with the two nebulizers.     

Comparison of experimental DPR and viscosity cross sections

It has previously been shown that the shape of the depolarized Rayleigh line in gases is governed by a correlation function exhibiting a spread in correlation times. Here it is shown that effective cross sections obtained from data on flow birefringence and the field dependence of the viscosity are in agreement with the DPR results. Moreover, the non-lorentzian behaviour of the H/p dependence of the viscosity, is fully interpretable in terms of the non-exponential behaviour of the DPR correlation function.     

Some effects of structural disorder on the optical properties of organic molecular crystals

We investigate the effects of structural disorder on the absorption line shapes of the lowest exciton states in molecular crystals at zero temperature by the application of the average t-matrix approximation to a system characterized by a gaussian distribution of site excitation energies. The line shape exhibits asymmetric line broadening with the high energy portion being close to lorentzian, while the low energy edge is sharp. The energy dependence of the low energy tail is determined by the dimensionality of the exciton band structure.     

Velocity dependence of impact line-broadening studied by resonant doppler-free two-photon laser spectroscopy

The velocity dependence of the collison broadening of the⁴⁰Ca 4s ^{2 1} S ₀→4s5p ¹ P ₁ →4s17d ¹ D ₂ transition by neon atoms has been studied. The experiment was performed exciting one velocity group of Ca atoms within the Doppler profile of the first transition and probing this group with a counterpropagating laser beam inducing the second transition. Using thermionic detection we have measured broadening rates for relative velocities between Ca and Ne atoms which corresponds to a temperature range of about 850 K (cell temperature) to 3000 K. The measured line-width was found to have very weak temperature dependence. This is attributed to the weak velocity dependence of polarization broadening of the final level which was found to be the major contribution to the broadening of the two-photon line. For large relative velocities significant asymmetries in the measured line profiles due to velocity changing collisions had to be taken into account.     

Temperature dependence of broadening and shifts of methane lines in the ν4 band

We have recorded high-resolution absorption spectra of methane broadened by dry air and by N₂ at temperatures from −63 to 41°C using a Fourier transform spectrometer. These spectra have been analyzed to determine pressure broadening and line-shift coefficients, along with their temperature dependences, for 148 lines in the ν₄ fundamental band of ¹²CH₄. The experimental uncertainties for lines with J″≤10 are generally <2% for the broadening coefficient b⁰_L, 6–12% for its temperature dependence exponent n, 6–20% for the line-shift coefficient δ⁰, and 20–40% for its temperature dependence coefficient δ′; for J″> 10 the experimental uncertainties are somewhat larger. These results, especially for N₂-broadening, are in excellent agreement with other recent measurements. Since the present results cover a wide range of rotational quantum numbers (J″ up to 14), the variation of the temperature dependence of the half-widths and shifts from line to line within the ν₄ band is also examined.     

Nucleation from supersaturated water vapors onn-dodecane substrate: A reverse Wilson chamber (RWC) method study

The reverse Wilson chamber method (RWC), developed for heterogencous nucleation investigation is applied to critical supersaturation measurements and determination of the surface concentration of nuclei (droplets) vs. supersaturation dependence in the case of nucleation from supersaturated water vapors onn-dodecane substrate. The experimental results obtained are interpreted in terms of the classical (Volmer) theory of heterogeneous nucleation as well as in the framework of the theory of barrierless nucleation. The several times lower critical supersaturations measured at four different temperatures, covering the range between 20° and 35° C, are explained by taking into account the effect of the negative line tension of three-phase contact. The temperature dependence of line tension for the three-phase systemn-dodecane/water/water vapor is extracted from the data to fir the theory. The results obtained are in complete disagreement with those ones obtained by Wu and Maa for the same system using jet-tensimeter technique, however, in another temperature interval. This discrepancy is discussed in detail in the text.     

State diagrams of partially crystalline polymer-good solvent systems: The isotactic polypropylene-m-xylene system

In the development of concepts according to which partially crystalline polymers are, in terms of phase state, microheterogeneous metastable liquids, a state diagram of the isotactic polypropylene-m-xylene system is obtained and discussed. It is shown that, in the absence of the limiting line in the diagram that reflects the temperature dependence of the liquid solubility in the partially crystalline polymer, no correct interpretation for the thermodynamic meaning of the temperature dependence of complete amorphization of such a polymer on the initial composition of a binary system (the liquidus curve) is possible.     

Investigation of radiation trapping in time resolved fluorescence spectroscopy

Time resolved fluorescence decay signals which are affected by radiation trapping usually do not show a pure exponential decay. These signals can be described by a sum of fractional signalsS _n originating from photons that were scattered exactlyn times before their detection. This gives a convincing physical interpretation of the total signal, especially in the case of polarized excitation where the nonexponential time dependence shows up very clearly. For comparison of experiments with theory the fractional signalsS _n were calculated by a Monte Carlo procedure including the angular dependence of each scattering process and an angle dependent frequency redistribution function. The good agreement between experiment and theory allows the determination of the natural lifetime with an accuracy of 10% from a single measurement. The influence of radiation trapping on a quantum beat signal is described quantitatively.     

Breakdown of the Born–Oppenheimer–Condon–Marcus approximation in long distance electron transfer

We consider the issue of how the breakdown of the Born–Oppenheimer–Condon–Marcus approximation affects the dependence of the electron-transfer rate k upon distance, as well as the dependences upon the driving force and temperature. For large distances, ca. r>10 Å, it is predicted that: (i) the slope of lnk vs r dependence decreases down to zero; (ii) the bell-shaped Marcus dependence upon the driving force is distorted, with the maximum shifting toward ΔG>0; and (iii) the apparent activation energy increases and the temperature dependence more and more declines from the Arrhenius form. These effects can be experimentally distinguished from similar effects due to other mechanisms, such as thermal activation of the electron transferred and temperature dependence of the reorganization parameters and driving force. Experimental data by Isied et al. [J. Phys. Chem. 97 (1993) 11456] on electron transfer between metal ions across rigid oligoproline bridges are well fitted using the present theory.