Two-Dimensional Infrared Spectroscopy From the Gas to Liquid Phase: Density Dependent J-Scrambling, Vibrational Relaxation, and the Onset of Liquid Character

Ultrafast 2DIR spectra and pump-probe responses of the N2O n 3 asymmetric stretch in SF6 as a function of density from the gas to supercritical phase and liquid are reported. 2DIR spectra unequivocally reveal free rotor character at all densities studied in the gas and supercritical region. Analysis of the 2DIR spectra determines that J-scrambling or rotational relaxation in N2O is highly efficient, occurring in ~1.5 to ~2 collisions with SF6 at all non-liquid densities. In contrast, N2O n 3 vibrational energy relaxation requires ~15 collisions, and complete vibrational equilibrium occurs on the ~ns scale at all densities. An independent binary collision model is sufficient to describe these supercritical state point dynamics. The N2O n 3 in liquid SF6 2DIR spectrum shows no evidence of free rotor character or spectral diffusion. Using these 2DIR results, hindered rotor or liquid-like character is found in gas and all supercritical solutions for SF6 densities ³ r * = 0.3, and increases with SF6 density. 2DIR spectral analysis offers direct time domain evidence of critical slowing for SF6 solutions closest to the critical point density. Applications of 2DIR to other high density and supercritical solution dynamics and descriptions are discussed. <br>

Two-Dimensional Infrared Spectroscopy From the Gas to Liquid Phase: Density Dependent J-Scrambling, Vibrational Relaxation, and the Onset of Liquid Character

Ultrafast 2DIR spectra and pump-probe responses of the N2O n 3 asymmetric stretch in SF6 as a function of density from the gas to supercritical phase and liquid are reported. 2DIR spectra unequivocally reveal free rotor character at all densities studied in the gas and supercritical region. Analysis of the 2DIR spectra determines that J-scrambling or rotational relaxation in N2O is highly efficient, occurring in ~1.5 to ~2 collisions with SF6 at all non-liquid densities. In contrast, N2O n 3 vibrational energy relaxation requires ~15 collisions, and complete vibrational equilibrium occurs on the ~ns scale at all densities. An independent binary collision model is sufficient to describe these supercritical state point dynamics. The N2O n 3 in liquid SF6 2DIR spectrum shows no evidence of free rotor character or spectral diffusion. Using these 2DIR results, hindered rotor or liquid-like character is found in gas and all supercritical solutions for SF6 densities ³ r * = 0.3, and increases with SF6 density. 2DIR spectral analysis offers direct time domain evidence of critical slowing for SF6 solutions closest to the critical point density. Applications of 2DIR to other high density and supercritical solution dynamics and descriptions are discussed. <br>

Nonlinear Vibrations of an Extensible Flexible Marine Riser Carrying a Pulsatile Flow

The influence of transported fluid on static and dynamic behaviors of marine risers is investigated. The internal flow of the transported fluid could have a constant, a linear, or a wave velocity. The riser pipe may possibly experience the conditions of high extensibility, flexibility, and large displacements. Accordingly, the mathematical riser models should be governed by the large strain formulations of extensible flexible pipes transporting fluid. Nonlinear hydrodynamic dampings due to ocean wave–pipe interactions implicate the high degree of nonlinearity in the riser vibrations, for which numerical solutions are determined by the state–space–finite-element method. It is revealed that the impulsive acceleration of internal flow could seriously relocate the vibrational equilibrium positions of the riser pipe. The fluctuation of the pulsatile flow relatively introduces the expansion of amplitudes and the reduction of frequencies of the riser vibrations. The pulsatile frequencies of the internal flow in wave aspect could reform the oscillation behavior of the conveyor pipe.

Concentration and Temperature Dependence of Laurdan Fluorescence in Glycerol

Steady-state and time-resolved fluorescence measurements have been performed on Laurdan, dissolved in viscous glycerol, as functions of temperature and concentration. The results indicate spectral heterogeneity of the Laurdan solution. The fluorescence decay time distribution is attributed to radiative deexcitation of spatial conformational forms of locally excited (LE) and charge transfer (CT) states, the S1(CT)EQ state being in thermodynamic and vibrational equilibrium. The lifetimes and contributions of the different fluorescence modes depend on concentration and temperature. The excitation and emission spectra show discontinuous changes with increase of the Laurdan concentration.We suppose that the observed changes are caused by the formation of Laurdan micelle aggregates.

Identification of chemical and vibrational relaxation regimes in rocket nozzle flow via a quasi-linear formulation

A quasi-linear formulation is proposed for high-speed finite-rate chemically reacting mixtures of imperfect gases, i.e. thermally perfect gases with specific heat varying with temperature, as an extension of a previously developed formulation for perfect gases. The form is suitable for application of accurate and fast algorithms. In particular, the resulting equations keep the same formalism already derived for reacting mixtures of perfect gases, thus indicating the potential for a straightforward extension of existing computational algorithms. In order to assess the applicability of the approach, the assumption of vibrational equilibrium needs to be verified. Accordingly, vibrational, as well as chemical, relaxation regimes are checked in a high expansion ratio rocket nozzle, indicating that the assumption under consideration is fully warranted. The effect of nozzle size on engine performance is also predicted.

Pseudostationary oblique shock-wave reflections in sulphur hexafluoride (SF 6 ): interferometric and numerical results

Pseudostationary oblique shock-wave reflections in SF 6 were investigated experimentally and numerically. Experiments were concluded in the UTIAS 10 x 18 cm Hypervelocity Shock Tube in the range of incident shock wave Mach number 1.25 < M s < 8.0 and wedge angle 4° < θ w < 47° with initial pressure 4 < P 0 < 267 Torr (0.53-35.60 kPa) at temperatures T 0 near 300 K. The four major types of shock-wave reflection, i. e. regular reflection (RR), single-Mach (SMR), complex-Mach (CMR) and double-Mach reflections (DMR), were observed. These were studied by using infinite-fringe interferograms from a Mach-Zehnder interferometer with a 23 cm diameter field of view. The isopycnics and the density distributions along the wedge surface are presented for the various types of reflection. The analytical transition boundaries between the four types of shock-wave reflection were established up to M s = 10.0 for frozen and equilibrium vibrational SF 6 . An examination of the relaxation length under the present experimental conditions indicated that a vibrational-equilibrium analysis was required. Comparisons of experiment with analysis for transition-boundary maps, reflection angle δ and the first triple-point trajectory angle X verify that the reflections were in vibrational equilibrium. The excellent agreement between the present interferometric results and the numerical results obtained by H. M. Glaz et al . ( Proc. int. colloq. on dynamics of explosives and reactive systems [ Berkeley ] (1985)) with real-gas effects also supports the vibrational equilibrium hypothesis for shocked SF 6 . The behaviour of the angle between the two triple-point trajectories ( X ' — X ) is discussed and the unique pattern of DMR with X ' = 0 was verified experimentally. A numerical analysis for the second triple-point system is obtained for the first time. It is shown that, for a given incident shock Mach number, the highest wedge-surface pressure is achieved through a DMR instead of an RR at high M s .