non-Boltzmann Distribution Research Articles

Neutral particle density modulation in the positive column of a low-pressure mercury discharge modulated at low frequencies: JR Riley, J Phys D, Appl Phys, 3 (8), 1970, 1226–1239

Degenerate four-wave mixing (DFWM) has been used to interrogate the nascent mercapto radicals (SH) emerging from photolysis of bulk-gas H2S samples at λdiss = 266 nm. These experiments reveal a ‘cold’ non-Boltzmann distribution of SH molecules formed exclusively in vibrationless levels of the X2Π ground electronic state, with a non-thermal population of spin-orbit states but no preference for lambda doublet components. Nearly all of the available energy appears as translational motion of the recoiling photofragments. Comparison with previous free-jet studies at λdiss = 193 nm shows the SH (ν = 0) rotational distribution to be relatively independent of photolysis wavelength and precursor rotational temperature.

Vibrational distribution of populations and kinetics of the CO–N2 system in the fundamental and harmonic regions

The vibroluminescence of carbon monoxide excited by activated nitrogen is investigated under high resolution in the fundamental and harmonic regions. The rotational population, corrected in some cases for self-absorption, shows a Boltzmann distribution characterized by a rotational temperature of 400 °K, but the vibrational population definitely shows a non-Boltzmann distribution which coincides very accurately with a Treanor-type distribution. This distribution is due, as explained by the theory of Treanor, to the anharmonicity of the molecules and to the inefficiency of the vibration–translation transfer. The variation of the number of vibrational quanta as a function of time allows a determination of the vibration–vibration rate transfer and shows the intervention of a deactivation process interpreted as due to CN radicals. Results in the harmonic region give ratios of the square of matrix elements which are compared with theoretical values and with other experimental values.

Magnetic resonance studies of optical spin polarization in triplet state anthracene

EPR studies of the lowest triplet state of anthracene in a phenazine host crystal reveal a non-Boltzmann distribution over the triplet spin levels of ≈1.5°K. Measurements of the lifetimes for each of the triple spin states provide information about both intramolecular decay processes and intermolecular triplet energy transfer mechanisms in the mixed crystal system.

Vibrational Relaxation of HBr(ν″ = 1) by HCl at 300 K

RECENT interest in chemical lasers has been strongly directed towards systems which give rise to vibrationally excited hydrogen halide molecules1–7. The efficiency of such systems will clearly depend on the rate at which vibrational energy is removed from the products of the chemical reaction, and considerable effort has been made to obtain the relevant rate data. Airey8 has described a pulsed laser system based on the reaction9,10 and has discussed the various energy transfer processes which may be involved. Moore et al. and Airey (see ref. 11) have further used reaction (1) to obtain rate data for the process. We have independently undertaken an extensive study of energy transfer processes involving the hydrogen bromide molecule using rather different techniques to monitor the vibrationally excited species and wish to report here rate data for the vibrational relaxation of HBr(ν″ = 1) by HCl. In our system, vibrationally excited HBr is produced by the fast reaction9,10 following the flash photolysis of HBr (pHBr = 33.3 Nm−2) in the presence of Br2 ( = 4.1 Nm−2), and excess Ar (pAr = 13.3 k Nm−2) to prevent a significant rise above room temperature (T = 300 K). Near resonant exchange processes rapidly reduced the initial vibrational distribution in HBr to a condition where a non-Boltzmann distribution in HBr(ν″ = 1) is observed. Relaxation from this level to ν″ = 0 can then be conveniently monitored, using kinetic absorption spectroscopy in the vacuum ultraviolet12, to observe the (0,1) transition of the strongly predissociated system connecting the ground state with “state [6]” (ν0 = 70,526 cm−1) (refs. 13, 14).

Fractional Brownian Motions, Fractional Noises and Applications

Fractional Brownian Motions, Fractional Noises and Applications

Relaxation by Vibration–Vibration Exchange Processes. Part II. Binary Mixtures

A previous paper on vibration processes in a pure gas is extended to the case of binary mixtures of gases. Through numerical integration of the master equation for vibrational relaxation, three distinct time scales to the relaxation processes are identified. The first time scale characterizes the pure-gas vibrational exchange reactions, the second relaxation time describes the coupling between species, while vibration–translation processes are characterized by a third time scale. Depending on the relative vibrational spacing and vibration–translation rates of the components in the mixture, vibrational distributions consistent with each of these time scales may be evident during the relaxation process. Through a steady-state analysis to the vibrational exchange terms in the master equation, it is demonstrated that large differences can exist between population factors (or vibrational temperatures in the harmonic model) for each species at steady state. Only at high kinetic temperatures (i.e., >1000°K) or for equilibrium conditions does vibrational coupling between the species in a mixture give rise to equal vibrational temperatures. In a binary mixture with T(vib) > T(trans), the species having the smallest vibrational spacing is described by higher vibrational temperatures than the second species, and this difference in vibrational temperatures increases with both decreasing kinetic temperature and mole fraction of the component with the smaller spacing. Non-Boltzmann distributions are predicted in the anharmonic model at steady state. However, it is shown that the harmonic treatment to the mixture coupling gives a reasonable zeroth-order solution. Comparison of the results with recent discharge flow data verify the mixture analysis and are consistent with the presence of non-Boltzmann distributions at steady state. More complete agreement must await better kinetic temperature measurements in the discharge flow environment.

Temperature and Density Measurements in Free Jets and Shock Waves

The fluorescence stimulated by a 17.5-kV electron beam probe was used to obtain measurements of rotational temperature and gas density in supersonic nitrogen jets expanding from room temperature. The parameter P0d (where P0 is the stagnation pressure in Torricelli and d is the orifice exit diameter in millimeters) was varied from 15 to 480 Torr-mm. Density measurements were made using an interference filter-photomultiplier combination. The experimental density data follow the axial isentropic density distribution in regions of rotational nonequilibrium. Rotational temperature measurements were obtained from rotational spectra of the 0–0 band of the N2+ first negative system. The experimentally determined rotational temperatures, which initially follow the axial isentropic temperature distribution in a free jet, depart from the isentropic curve at low temperatures and freeze at a constant value, indicating a substantial degree of nonequilibrium in the expansion. A shock holder was inserted in the jet and a number of shock waves in the range M = 4 to M = 15 were investigated. Rotational spectra indicate a large departure from a Boltzmann distribution in the rotational levels in the center of a shock front. An apparent non-Boltzmann rotational distribution in the jet expansion was also observed.

Gas-Phase Electron Resonance Spectra of Fluorine and Chlorine Atoms in Their Ground (P322) and Excited (2P½) Electronic States

The gas-phase electron resonance spectra of fluorine and chlorine atoms in their ground (P322) and excited (2P½) states are described. Fluorine atoms are formed by passing CF4 through a microwave discharge; the P322 spectrum shows six strong lines and five weaker lines, three of the latter being previously unreported and arising from ΔMF=0 transitions. Two lines of the 2P½ spectrum are detected and their intensity relative to that of the ground-state spectrum indicates a non-Boltzmann distribution between the P322 and 2P½ states. Chlorine atoms are formed by passing CF3Cl or CF3Cl/Cl2 mixtures through a microwave discharge. In addition to the intense 35Cl and 37Cl P322 spectra, four weak lines arising from excited 35Cl 2P½ atoms are detected. The intensities of these lines also indicate a non-Boltzmann distribution between the ground and excited states.

Cross-sections for deactivation of Hg (63 P 0)

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