Critical and sustainable fluxes: theory, experiments and applications

Over the last ten years, numerous membrane filtration data have been viewed in the light of the concept of critical flux. This concept, used in a number of different ways often without explicit redefinition, is here clarified both from a theoretical and from an experimental viewpoint. Also, a link is make with the sustainable fluxes. Also covered are the various methods of measurement and the influence of membrane and suspension properties on the critical flux. Over the same period of time, models have been developed to explain the observed behaviour. Those for stable colloidal suspensions are based on the existence of repulsive interactions between soft matter constituents. The assumptions and usefulness of various models are discussed. The concept of a critical concentration for phase transition is introduced into the theoretical discussion. For theoreticians and experimentalist, this and the clarified concept of a small set of critical fluxes will continue to provide a valuable framework. For membrane users dealing with most industrial process streams (mixtures and complex fluid) the concept of a sustainable flux (shown as being derived from critical flux) is of a great utility; above a certain key flux (dependent on hydrodynamics, feed conditions and process time) the rate of fouling is economically and environmentally unsustainable. For many, knowledge of the point below which no major irreversible fouling occurs (the critical flux) in a membrane separation will always be of greatest utility

A Ligand Field Theory View Of The Electronic Structure Of Cax (x=f, Cl, Br, I, And O)

The CaX family of diatomic molecules illustrates concepts developed by inorganic chemists to rationalize the properties of metal-centered complexes. The basic idea is that an atom or an atomic-ion is surrounded by ligands, and that the electronic properties of the complexes are dealt with in a model in which the central metal atom and the ligands are treated as retaining their separated atom or molecule properties perturbed by identifiable and quantifiable metal-ligand interactions. Ligand Field Theory is \textit{semi-empirical} in the sense that it is a framework for building a systematic understanding of the properties of families of complexes from spectroscopic measurements of the properties of the separated species and the interactions between them. The electronic structures of the CaX molecules are described by atomic-ions-in-molecule ligand field models. The Ca atom is treated as Ca$^{+}$ with a single electron in the 4s$\sigma$ , 4p$\sigma$ or $\pi$, or 3d$\sigma$,$\pi$, or $\delta$ orbital For X=F, Cl, Br, and I, the ligand is a closed-shell halide ion. For X=O, the ligand is an open-shell O$^{-}$ ion with a single hole in the p$\pi$ ($\pi$$^{-1}$) or $p\sigma$ ($\sigma$$^{-1}$) orbital. The building blocks of the electronic structure model are known by different names in the inorganic chemistry, small-molecule spectroscopy, and quantum chemistry communities. Fine structure (spin-orbit, spin-spin, spin-rotation, and lambda-doubling) and spectroscopic perturbation matrix elements (spin-orbit and L-uncoupling) report on the CaX electronic structure

Observation of b2_2 symmetry vibrational levels of the SO2_2 \tilde{\mbox{C}} 1^1B2_2 state: Vibrational level staggering, Coriolis interactions, and rotation-vibration constants

The $\mathrm{\tilde{C}}$ $^1$B$_2$ state of SO$_2$ has a double-minimum potential in the antisymmetric stretch coordinate, such that the minimum energy geometry has nonequivalent SO bond lengths. However, low-lying levels with odd quanta of antisymmetric stretch (b$_2$ vibrational symmetry) have not previously been observed because transitions into these levels from the zero-point level of the $\mathrm{\tilde{X}}$ state are vibronically forbidden. We use IR-UV double resonance to observe the b$_2$ vibrational levels of the $\mathrm{\tilde{C}}$ state below 1600 cm$^{-1}$ of vibrational excitation. This enables a direct characterization of the vibrational level staggering that results from the double-minimum potential. In addition, it allows us to deperturb the strong $c$-axis Coriolis interactions between levels of a$_1$ and b$_2$ vibrational symmetry, and to determine accurately the vibrational dependence of the rotational constants in the distorted $\mathrm{\tilde{C}}$ electronic state

On the understanding and feasibility of “Breakthrough” Osmosis

Osmosis is the movement of solvent across a permselective membrane induced by a solute-concentration gradient. Now in ‘Forward Osmosis’ it is empirically observed that the diffusion of the solute is counter to that of the solvent i.e. there is so-called “reverse salt diffusion”. However it has been recently suggested, in a theoretical paper, that if allowance is made for minor deviations from ideal semi-permeability then operation in an overlooked mode of “breakthrough” osmosis would be possible and importantly it would yield relatively large rates of osmosis. A consequential prediction was that in “breakthrough mode”, Pressure-Retarded Osmosis (PRO) would generate very high power densities exceeding those in the conventional mode by one order of magnitude. The practicality of this suggestion was explored and necessarily questions were then raised regarding the foundation of the Spiegler-Kedem-Katchalsky model

Probing cis-trans isomerization in the S1 state of C2H2 via H-atom action and hot band-pumped IR-UV double resonance spectroscopies

We report novel experimental strategies that should prove instrumental in extending the vibrational and rotational assignments of the S1 state of acetylene, C[subscript 2]H[subscript 2], in the region of the cis-trans isomerization barrier. At present, the assignments are essentially complete up to ∼500 cm[superscript −1] below the barrier. Two difficulties arise when the assignments are continued to higher energies. One is that predissociation into C[subscript 2]H + H sets in roughly 1100 cm[superscript −1] below the barrier; the resulting quenching of laser-induced fluorescence (LIF) reduces its value for recording spectra in this region. The other difficulty is that tunneling through the barrier causes a staggering in the K-rotational structure of isomerizing vibrational levels. The assignment of these levels requires data for K values up to at least 3. Given the rotational selection rule K' − ℓ" = ± 1, such data must be obtained via excited vibrational levels of the ground state with ℓ" > 0. In this paper, high resolution H-atom resonance-enhanced multiphoton ionization spectra are demonstrated to contain predissociated bands which are almost invisible in LIF spectra, while preliminary data using a hyperthermal pulsed nozzle show that ℓ" = 2 states can be selectively populated in a jet, giving access to K' = 3 states in IR-UV double resonance.United States. Department of Energy (Grant No. DE-FG0287ER13671)Chinese Academy of Sciences (Distinguished Visiting Professorship)Natural Sciences and Engineering Research Council of Canada (NSERC

Edge effects in chirped-pulse Fourier transform microwave spectra

Recent applications of chirped-pulse Fourier transform microwave and millimeter wave spectroscopy have motivated the use of short (10–50 ns) chirped excitation pulses. In this regime, individual transitions within the chirped pulse bandwidth do not all, in effect, experience the same frequency sweep through resonance from far above to far below (or vice versa), and “edge effects” may dominate the relative intensities. We analyze this effect and provide simplifying expressions for the linear fast passage polarization response in the limit of long and short excitation pulses. In the long pulse limit, the polarization response converges to a rectangular function of frequency, and in the short pulse limit, the polarization response morphs into a form proportional to the window function of the Fourier-transform-limited excitation pulse.United States. Dept. of Energy. Office of Basic Energy Sciences (DE-FG0287ER13671

JON HOUGEN'S MONOGRAPH NBS 115

I was a graduate student in the Klemperer group in 1970 when Jon Hougen's "The Calculation of Rotational Energy Levels and Rotational Line Intensities in Diatomic Molecules" appeared. Physical Chemists like to break stuff. My favorite topic, spectroscopic perturbations, presents a rich variety of broken patterns. I began as a collector and NBS 115 both gave me tools to add to my collection and a challenge to look beyond molecular constants. My perturbations were more than molecules behaving badly. The 49 pages of NBS 115 became the foundation of my career as a spectroscopist. Jon Hougen wrote defining guides for many areas of spectroscopy, thereby providing the foundations for many careers. Each such guide echoed the elegant simplicity of NBS 115

DIRECT POTENTIAL FIT FOR THE X1Σ STATE OF F2: PERTURBATION OF THE HIGHEST OBSERVED V=22 VIBRATIONAL LEVEL

The high-resolution vacuum-uv spectrographic data$^{1}$ for the C - X emission and C,(D,E),H,h,I - X(v = 0) absorption transitions of F$_{2}$, in combination with pure rotation$^{2}$ and vibration-rotation$^{3}$ Raman data, have been employed in a least-squares analysis. Attention was given to the extensive blending in the absorption data and to account for plate-to-plate shifts in the emission data. The C - X data, with an estimated uncertainty of 0.05 \wn, sample X state vibrational levels v = 1 - 22,for which the potential energy function was fitted using the extended-MLR model$^{4}$. 3549 line positions in the weighted fit provided estimates of 1303 term values of excited electronic states and 17 parameters for the ground state. The highest observed v = 22 level of the ground state, which lies only 114 \wn below the F($^{2}$P$_{3/2}$) + F($^{2}$P$_{3/2}$) dissociation limit, is found to be perturbed; all rotational levels (J = 0 - 19) lie at energies 5 - 13 \wn below their expected positions. A deperturbation model was employed within the direct potential fit; in this novel approach, the eigenvalue of each J-level in v = 22 was determined from a 2 x 2 matrix, with the diagonal level of the perturbing state represented by E$_{p}$ + B$_{p}$J(J+1), and the off-diagonal element by a + b(J + 1/2). However, the b-parameter was indeterminate; a successful fit of the entire data set with inclusion of the deperturbation model for v = 22 provided the estimates E$_{p}$ = -70.5(3.7) \wn, B$_{p}$ = 0.226(6) \wn, a = 16.2(8) \wn and R$_{e}$ = 1.412555(4)\AA. There is much interest in an identification of the perturbing state. The results indicate a J-independent spin-orbit interaction with a weakly-bound perturbing state (R$_{e}$ = 2.8\AA), lying 40 - 50 \wn above v = 22. The absence of a J-dependent b(J + 1/2) Coriolis interaction implies a perturber with 0$_{g}$$^{+}$ symmetry. A plausible candidate is the a'(0$_{g}$$^{+}$) state which dissociates to the same atomic limit and which is repulsive at short-R. 1. E.A. Colbourn, M. Dagenais, A.E. Douglas, J.W. Raymonda, Can. J. Phys. 54 (13) (1976) 1343-1359. 2. H.G.M. Edwards, E.A.M. Good, D.A. Long, J. Chem. Soc. Faraday Trans. 272 (1976) 984-987. 3. R.Z. Martinez, D. Bermejo, J. Santos, P. Cancio, J. Mol. Spectrosc. 168 (1994) 343-349. 4. R.J. Le Roy, N.S. Dattani, J.A. Coxon, A.J. Ross, P. Crozet, C. Linton, J. Chem. Phys. 131 (2009) 204309

It is all about phase and it is not star trek

The marriage of chirped pulse millimeter-wave spectroscopy with a buffer gas cooled molecular beam source has yielded an increase in spectral velocity (number of resolution elements per unit time) of a factor of one million! But it gets even better. Essential information is encoded not just in the frequencies of the transitions, but also in the relative intensities and especially phases of the transitions. Transitions between Rydberg states of atoms and molecules are an ideal test ground for techniques that fully exploit these newly accessible observables

Collisional depolarization of state selected (J,M J ) BaO A 1Σ+ measured by optical–optical double resonance

The optical–optical double resonance (OODR) technique is used to investigate the change in magnetic quantum number (M) a state selected molecule undergoes on collision with other molecules. A first linearly polarized dye laser prepares A  1Σ+BaO(v = 1) in the J = 1, M = 0 sublevel. The extent of collisional transfer to other M sublevels of both J = 1 and J = 2 is then probed by a second polarized dye laser which induces fluorescence from the C  1Σ+ state. Elastic collisions (ΔJ = 0) between BaO (A  1Σ+) and CO2 are observed to change M from 0 to ±1 leaving J unchanged. The total elasticM‐changing cross section is σΔM CO2 = 8.4±2.4 Å2. Inelastic collisions (ΔJ = +1’ which transfer molecules to j = 2 also cause M changes. with both Ar and CO2 as collision partners. M, the s p a c e‐f i x e d projection of J, is found to be neither conserved nor randomized. Quantum atom–diatom collision models with quantization axis along the relative velocity vector are considered. Transition amplitudes in this system are evaluated using the l‐dominant and CS approximations