Vibrational relaxation of oxygen in an argon cage

The vibrational relaxation of oxygen embedded in an argon cage through vibrational to local translation, rotation, and argon phonon modes has been studied using semiclassical procedures. The collision model is based on the trapped molecule undergoing the restricted motions (local translation and hindered rotation) in a cage formed by its twelve nearest argon neighbors in a face-centered-cubic structure. At 85 K in the liquid argon temperature range, the deexcitation probability of O(2)(v=1) is 5.8 x 10(-12) and the relaxation rate constant with the collision frequency from local translation is 23 s(-1). The rate constant decreases to 5.1 s(-1) at 50 K and to 0.016 s(-1) at 10 K in the solid argon temperature range. Transfer of the vibrational energy to local translation, rotation (both hindered and free), and argon phonon modes is the relaxation pathway for the trapped oxygen molecule.     

Dielectric relaxation in styrene-related polymers at low temperatures

The complex dielectric constants ?^* = ?′ ? j?″ of each of several members of a system of copolymers of 4-chlorostyrene and 4-methylstyrene have been measured from 1.6°K to 300°K and from 0.1 kHz to 20 kHz. The principal experimental findings are: the strength of the relaxation process which occurs near 50°K at 1 kHz varies linearly with changing copolymer composition; both the apparent activation energy (H = 2.7 ± 0.7 kcal/mole) and the shape of the relaxation curve are independent of the composition variable and of the temperature (or frequency) within the ranges studied; and the ratio of the relaxation strength of poly-4-methylstyrene to that of poly-4-chlorostyrene in the 50°K process is about 25 times the corresponding ratio for the primary relaxation process that occurs in the neighborhood of the glass-transition temperature. These findings suggest that in the 50°K process the phenyl groups relax independently of one another; that the apparent activation energy and the shape of the relaxation spectrum are determined primarily by the nature of the intrachain forces; and that the strength of the relaxation process depends primarily on effects of intermolecular forces that are governed by the molar “free volume” of the copolymers.     

Vibrational relaxation of DF at low temperatures

Temperature dependence of the probability of the deexcitation process DF(ν = 1) + DF(ν = 0) → DF(ν = 0) + DF(ν = 0) has been investigated near and below room temperature based on the model that the vibrational energy is transferred to the hindered rotational (oscillatory) motion as well as the translational motion. The deexcitation probability increases sharply with decreasing temperature; this inverse temperature dependence is attributed to the important contribution of hydrogen-bond attraction.     

The second virial coefficient of argon at low temperatures

We present experimental data of second virial coefficients of argon at temperatures of 77.3, 87.2 and 90.2 K. The results are in excellent agreement with theoretical values.     

Restricted intramolecular vibrational relaxation in polyatomics and laser selective effects

A theory for unimolecular dissociation applicable to selective laser excitation is presented. Expressions for lifetimes, yields, and product fragment translational energy distributions are given as a function of IVR rate. We analyze an experiment purporting to “ demonstrate” rapid IVR.     

A new relaxation process in the high-elastic state at low temperatures

A new relaxation process, explaining the change of elasticity in rubberlike polymers at critical stress (0.1?0.5 kgf/cm²) has been discovered. This process is characterized by the low value of activation energy (weak temperature dependence of relaxation times) and large sizes of kinetic units (strong dependence of relaxation time on stress). Critical stress depend on temperature and for rubberlike polymers turns to zero at 40°?60°C. Mechanism of the phenomena can be explained by the existence of the ordered molecular microregions, creating additional crosslinking points of nonchemical nature with free chains of the network, breaking up at critical stress. Observed phenomena is analogous to the process of forced rubber elasticity of those polymers in glassy state. Critical stress is analogous to the limit of forced rubber elasticity below glass transition temperature.     

Compression stress relaxation in carbon black reinforced HNBR at low temperatures

Findings of a study of stress relaxation behaviour of hydrogenated nitrile butadiene rubber (HNBR) at nominal compressive strains up to 0.4 and temperatures above and below the glass transition temperature T_g are reported. Two formulations of a model HNBR with 36% acrylonitrile content and carbon black (CB) loading of 0 and 50 phr were investigated. The relaxation function of HNBR is found to be independent of strain at temperatures right above the T_g or at times longer than 10⁻³ s for the deformations employed. CB imparts higher long-term stiffness and also larger relaxation strength at times longer than 10⁻⁴ s to the HNBR, but it does not affect the relaxation behaviour of the rubber in the time span from 10⁻³ – 10⁴ s. In addition, the relationship between the strain energy function of HNBR and temperature is demonstrated to have a complex concave-downward shape which is affected by two competing contributions of entropy elasticity and the stress relaxation.     

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.     

Manifestation of intramolecular vibrational energy redistribution on electronic relaxation in large molecules

Some universal characteristics are discussed of the decay lifetimes and fluorescence quantum yields from the S₁ manifold of large molecules, which originate from the coupling between intrastate vibrational energy redistribution and interstate electronic relaxation. The time-resolved total fluorescence decay from the S₁ state of jet-cooled 9-cyanoanthracene exhibits non-exponential decay in the energy range E_v= 1200–1740 cm⁻¹ above the S₁ origin, which does not originate from dephasing but rather manifests the effects of intrastate intermediate level structure for vibrational energy redistribution on intersystem crossing.     

Proton-pair disorder in dimers of aromatic carboxylic acids: vibrational spectra of benzoic acid at low temperatures

The resolved multiplet structure of carboxylic ring bands observed for benzoic acid and d₅-deuterated benzoic acid by IR and Raman spectroscopy at low temperatures is not in agreement with previous assignments. The temperature dependence of half-widths of some other vibrational bands reveals that more than one mechanism for proton-pair disorder has to be taken into account.     

Solvent dependence of OH bend vibrational relaxation of monomeric water molecules in liquids

The vibrational relaxation rates of the OH bending mode of monomeric H(2)O molecules diluted in various liquid halogenated methane and ethane derivates have been determined by a picosecond infrared pump-probe study. Relaxation time constants between 4.8 and 40.5 ps have been obtained. The discussion of the general solvent dependence suggests that in all cases the solvent fundamental with the smallest energy mismatch is favorably populated by this intermolecular energy transfer process.     

Initial state selection and intramolecular vibrational relaxation in reacting polyatomic molecules. Isopropylcyclobutane precursor

The study of intramolecular vibrational energy transfer in polyatomic molecules excited to the level of chemical reaction is here extended to hydrocarbon species. By insertion of ¹CH₂ into the CH bonds of isopropylcyclobutane a closely related series of chemically activated alkyl cyclobutanes are produced at levels of excitation above 100 kcal mole^?1. The cyclobutane ring decomposes into olefin fragments. The methylene insertion takes place at CH sites on the molecule which are either on the ring or on the side chain. This corresponds to injection of excited molecules into various regions of their energy-coordinate hyperspace which are more or less adjacent to, or remote from the critical hyperplane corresponding to decomposition. A study of the pressure dependence of the relative rates and amounts of decomposition of the several differentially excited cyclobutanes follows theoretical expectations with regard to occurrence of non-randomized decomposition from some of the molecules prior to complete relaxation. Molecules which have been activated on the side chain exhibit only ordinary randomized decomposition. Analysis of the data on a simple model leads to gross rates of intramolecular relaxation, λ = 2.2 × 10¹²s^?1 and λ = 3.5 × 10¹²s^?1, for species excited at different sites on the ring. These rates are several times larger than those previously reported for fluorocyclopropanes.     

Spin-lattice relaxation of some polymer radicals of the peroxide type at low temperatures

At a frequency of 9300 Mc, the relaxation phenomena have been studied for radicals of the type R-OO in the lattices of the polymers-(CF₂)_n-,-(CF₂CFCl)_n-and-(CF₂CFH)_n-for polycrystalline specimens at liquid helium and liquid hydrogen temperatures. At liquid helium temperatures, strongly marked spin-spin cross-relaxation effects are observed. A model for the relaxation mechanism is presented which satisfactorily explains the data obtained.     

Initial state selection and intramolecular vibrational relaxation in reacting polyatomic molecules. Neopentylcyclobutane precursor

In order to confirm and extend the kinetic and intramolecular vibrational relaxation features observed in the isopropylcyclobutane system (KR), the sub     

The competition between optical pumping and intramolecular vibrational relaxation in organometallics: A new chromium Rydberg series

We have measured the multiphoton ionization spectra of Cr(CO)₆, Cr(CO)₃C₆H₆, Cr(CO)₃C₆H₅Cl, and Cr(CO)₃C₆H₅CH₃ in the region 355–365 nm. We have identified previously unassigned features, in particular, an even-parity ⁷S₃ Rydberg series of neutral bare chromium atoms. From the assignment we have obtained an improved value for the ionization potential, the quantum defect and evidence for electron correlation and nuclear screening effects in the bare chromium atom. Coupled with assignments of other nearby spectral features we have also obtained the first evidence of intramolecular vibrational redistribution (IVR) competing with multiphoton up-pumping of organometallic molecules.