A shock tube study of vibrational relaxation in SO2, SO2Ar and SO2He

Vibrational relaxation times in SO₂, SO₃Ar (11%, 20% and 54% SO₂) and SO₂He (9.5% SO₂) were measured behind incident shock waves using the laser schlieren technique in the temperature ranges 550–1200 K, 700–2100 K and 700–1600 K respectively for the three systems. An analysis of the density gradient signals revealed a double exponential behaviour consistent with earlier studies. The fast relaxation rates were not quantitatively studied and the slow relaxation rates were found to fit the following equations:

where Pτ is the relaxation time in atm μs and T is in °K. The collision numbers corresponding to the slower rates were found to agree well with a recent theoretical calculation using SSH-Tanczos theory.     

Relaxation phenomena involved in the L3M4,5M4,5;1G4 auger process in zinc metal

A detailed analysis is presented of the L₃M_4,5M_4,5;¹G₄ Auger transition in metallic zinc. An extra-atomic relaxation term, neglected until now, is taken into account. This results in excellent agreement between calculated and experimental values of the Auger-transition energy.     

Detailed analysis of the L3M4,5M4,5; 1G4 Auger transition in atomic zinc: Improved Auger energy calculations

A hitherto neglected relaxation term is introduced in the calculation of Auger electron energies. The agreement between the theoretical L₃M_4,5M_4,5; ¹G₄ Auger energy in atomic zinc and the experimental value of Aksela and Aksela is excellent. Relaxation energies are determined by means of OHFS hole state calculations.     

Vibrational relaxation in SO2

SSH—Tanczos calculations are carried out to estimate the energy transfer probabilities and the slow vibrational relaxation time in SO₂ in the temperature range 300–2000 K. The theoretical results suggest a series process below 1000 K, and a complex series/parallel process above that temperature for the vibrational relaxation in SO₂. The theoretical results are compared with the known experimental data.     

Relaxation in a Na/Na2 nozzle expansion

Atom—molecule collisions in a Na/Na₂ nozzle expansion are investigated. The atoms are marked near the nozzle exit by preparing them alternatively into the 3²S and 3²P state. The effect of collisions between these atoms and the molecules is studied far downstream the beam. We find that the internal energy distribution of the molecules depends on the internal energy of the atoms. The specific change of the internal energy distribution gives information on the energy relaxation in the nozzle expansion.     

Photoluminescence dependence on imposing bias for ZnGa2O4 and ZnGa2O4 activated with Mn or Cr n-type semiconductor electrodes

Photoluminescence (PL) dependence was investigated by imposing cathodic and anodic bias for ZnGa₂O₄, ZnGa₂O₄:Mn and ZnGa₂O₄:Cr n-type semiconductor electrodes. Under the cathodic bias PL intensity was weak at about 1/3 times compared with imposing no bias, while under the anodic bias the intensity was strong at about 2 times maximally by using the ZnGa₂O₄:Mn and ZnGa₂O₄:Cr electrodes although no change about the intensity was observed by using the ZnGa₂O₄ electrode. These results suggest that the emission attributed to recombination between electrons and holes is decreased by flow of cathodic current under the cathodic bias while the emission is increased to decrease at non-radiative transition rates under the anodic bias when the energy relaxation occurs.     

35Cl NQR and 1H NMR studies of [C(NH2)3]AuCl4, [C(NH2)3]2PtCl4, and [C(NH2)3]2PdCl4

The temperature dependence measurements of ³⁵Cl NQR frequencies and ¹H NMR spin-lattice relaxation time T₁ were carried out for guanidinium tetrachloro-aurate(III), -platinate(II), and -palladate(II). The gold(III) complex showed four NQR lines at various temperatures between 77 and 344 K, while the platinum-(II) and palladium(II) complexes gave two NQR lines in the temperature ranges 77–169 K and 77–220 K, respectively. An unusual phase transition was located at 363 K for the gold(III) complex. The high-temperature phase was easily supercooled. All the complexes studied yielded a T₁ minimum attributable to the reorientation of the planar cation about its C₃ axis. The motional parameters were evaluated. The Zeeman-quadrupole cross relaxation between protons and chlorine nuclei was observed for the platinum(II) and palladium(II) complexes at various temperatures below room temperature, while it was also detected for the high-temperature phase of the gold(III) complex.     

Vibrational relaxation in COF2 and Xe,C2H6 mixtures following intense laser excitation

The VR,T rate in COF₂ was measured directly by the ultrasonic absorption technique. The laser-induced fluorescence method was used to study VV exchange between the strongly pumped ν₂, ν₁ manifold and other vibrational degrees of freedom. At a few Torr a transition of the μm fluorescence from a single exponential decay to a relaxation spectrum is observed. This relaxation spectrum was analyzed by determining the “differential decay rate” for successive small time intervals. The relaxation spectrum is not changed by a pressure increase from ≈ 4 to 15 Torr. Similarly, relatively large amounts of Xe must be added before a change in the relaxation behavior of COF₂ can be detected. C₂H₆ is a very effective quencher of the 5μm fluorescence.     

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.     

Very long vibrational lifetimes in liquid O2 and N2

Via stimulated Raman scattering the first vibrational energy level is excited above the thermal equilibrium value. Using an optical Schlieren method the vibration-translation relaxation times are measured to be 50 μs and 1 ms in liquid O₂ and N₂, respectively.     

Proton motion in HNbO3 and HTaO3

Proton NMR relaxation times T₁, T_1?, and T₂ are reported for the compounds HTaO₃ and HNbO₃ in the temperature range 170–540 K. The data show that for both compounds two types of motion occur. Proton diffusion occurs in both compounds above 400 K with a correlation time, τ⁰_c, of ～30 ps and an activation energy of ～50 kJ mole^?1, approximately twice that for the localized process occurring at lower temperatures. Alternating current conductivity measurements have been used to study proton diffusion above 470 K in these compounds.     

Triplet annihlation in pyrene-d10 doped fluorene

Triplet exciton concentration inferred from delayed fluorescence measurements of pyrene-d₁₀ doped fluorene crystals has been examined as a function of temperature in order to study the correlation between exciton density and electronic triplet spin lattice relaxation (T_ie). The results have indicated a poor correlation between the delayed fluorescence intensity and the electronic relaxation rate although a qualitative correlation exists between the growth of trap phosphorescence and relaxation rate.     

Dielectric and impedance properties of Sr(Sm0.5Nb0.5)O3 ceramics

Perovskite types Sr(Sm_0.5Nb_0.5)O₃, (SSN) ceramics have been prepared through solid state reaction route. The scanning electron microscopy provides information on the quality of the samples and uniform grain distribution over the surface of the samples. The field dependence of the dielectric response was measured in a frequency range from 50 Hz to 1 MHz and in a temperature range from 60 °C to 420 °C indicates polydispersive nature of the materials. An analysis of the dielectric constant (?′) and tangent loss (tanδ) with frequency is performed assuming a distribution of relaxation times as confirmed by the scaling behavior of electric modulus spectra. The frequency dependence of the electric modulus peak is found to obey Arrhenius law with activation energy of ∼0.026 eV. The complex plane impedance plot shows the grain boundary contribution for higher value of dielectric constant in the law frequency region. The frequency dependence of electrical data is also analyzed in the framework of conductivity and electric modulus formalisms. Both these formalisms show qualitative similarities in relaxation times. The scaling behavior of imaginary part of electric modulus M″ suggests that the relaxation describes the same mechanism at various temperatures in SSN.     

Vibrational relaxation of CF4 at low temperatures

An apparatus for low temperature acoustic measurements is described. The vibrational relaxation times of CF₄ have been determined between 183 K and 295 K, and the mechanism of vibrational energy transfer in this molecule is discussed.     

The laser sensitized reaction SF26 + NO + O3

A pulsed CO₂ laser was used to irradiate a rapidly flowing mixture of NO, O₃, and SF₆. When the laser was tuned to an SF₆ absorption line, an increase in the visible NO^*₂ emission was observed. The laser-induced signal has two unusual features. First, the rise time is much longer than is observed when O₃ is excited directly, and, second, the signal decays to a value above the original baseline. The rise rate is attributed to VV energy transfer from SF²₆ to O₃, while the baseline shift is attributed to a temperature jump resulting from rapid non-resonant VV relaxation within the SF₆ molecule. Both the size of the T-jump and the fraction of vibrationally excited ozone molecules vary inversely with NO pressure.     

Franck—condon factors of the T1 ↷ S0 radiative and nonradiative transitions of naphthalene-h8 and -d8-a correlation function analysis

Franck—Condon factors for the T₁ ? S₀ transition in naphthalene-h₈ and naphthalene-d₈ are calculated employing the correlation function approach which allows us to investigate the distribution of the released electronic energy among the normal modes of the Final ground state. The relevant coupling parameters relating to geometry, frequency and anharmonicity changes due to excitation are included. Those related to geometry changes are obtained from the vibronic intensities of the phosphorescence spectrum as well as from a calculation implementing a semi-empirical relation between bond order and bond length. The calculated nonradiative rates compare well with the experimental rates in terms of absolute magnitude and deuterium effect. The semi-empirical calculations of the ribtonic intensities provide detailed information about force fields that are otherwise indistinguishable on the basis of their ability to reproduce infrared frequencies.     

Vibrational relaxation of highly excited molecules: VV transfer from SF6 to N2O

Vibrational energy transfer from SF₆ to N₂O was studied as a function of SF₆ vibrational energy. The intensity, rise time and decay time of N₂O fluorescence increased monotonically with the level of donor excitation. The observations are consistent with a mechanism that is not mode specific, with donor VT relaxation faster than intermolecular VV transfer.     

Comparisons of energy disposal by the reactions of H atoms with Cl2, SCl2, S2Cl2 and SO2Cl2 from observation of HC1 infrared chemiluminescence

Arrested relaxation infrared chemiluminescence studies of the H + Cl₂, SCl₂, S₂Cl₂, SOCl₂ and SO₂-Cl₂ reactions have been made. The mean fraction of vibrational (stational) energy released to HCl is 0.40 (0.10); 0.40 (0.13); 0.38 (? 0.02); 0.33 (?0.02) and 0.36 (?0.02) for the series. Only the H + SCl₂ reaction shows a two component initial rotational distribution. The larger (f_V) and (f_R) from H + SCl₂, relative to the other polyatomic reagents, is consistent with the observation that this is the only reaction that shows forward scattering. The room temperature rate constants also were measured, relative to H + Cl₂, and were found to decline in the series from 0.68 for SCl₂ to 0.02 for SO₂Cl₂. All of these data support the suggestion (first made by Heydtmann and Polanyi) that the unusual rotational energy disposal pattern from H + SCl₂ is a consequence of migration of H from the initially encountered C1 to the second C1, which then forms the HCI product; this pathway augments the direct reactive pathway, which gives HCI in lower J states.     

Electronic transport properties and electrically induced p-n junction in ZrO2 + 10 m/o Y2O3

Through the application of voltages to cubic ZrO₂, stabilized by 10 m/o Y₂O₃, using a nitrogen/Ag and an air/Pt electrode, concentration gradients of the electronic species and p-n junctions in the sample have been created. The transient relaxation of the voltage is investigated and is interpreted in terms of the mobilities of both excess and defect electrons between 700 and 900°C. The movement of the p-n junction is characterized by a shoulder-type voltage-time relation. At 900°C the mobilities of the electrons and holes are 2.3 × 10^?2 and 1.5 × 10^?4 cm²/Vsec, respectively. The activation energy of transport is much smaller for the excess electrons than the holes. The electronic conductivities are determined from the steady-state polarization current.     

Fluorine core esca linewidths in CH3F and CF4

Ab initio calculations within the Hartree-Fock formation have been carried out on potential energy surfaces of the ground and the F_1s hole states of CH₃F and CF₄ in order to investigate linewidths of their ESCA spectra. The calculations show that potential energy surfaces of both hole states have dissociative character and can be approximated by straight lines in the region of interest. A simple formula for the ESCA fwhm linewidth is derived which yields results in good agreement with experiment. Theoretically derived relaxation and Koopmans' energies have been investigated as a function of geometry.