Do ‘Quark-Stars’ Exist?

Possible existence of quark-matter in dense neutron-stars is discussed using Quantum Chromodynamical equation of state for cold degenerate quark-matter.     

Laser Running Waves for the Kapitza–Dirac Diffraction in the Atom Interferometer

The scheme of multi-momentum atom interferometer based on the resonant Kapitza–Dirac diffraction is considered. The conclusion is made that the arms of counter propagating waves forming the standing wave, which scatters the atoms, should have the equal length.     

Is 4‐nitrobenzenethiol converted to p,p′‐dimercaptoazobenzene or 4‐aminothiophenol by surface photochemistry reaction?

For the first time, the experimental and theoretical evidence for the conversion of 4‐nitrobenzenethiol (4‐NBT) to p,p′‐dimercaptoazobenzene (DMAB) in Ag and Cu sols by surface photochemistry reaction is obtained with surface‐enhanced Raman scattering (SERS) spectroscopy. The SERS spectrum of 4‐NBT in Cu sol is identical to that of DMAB produced from 4‐aminothiophenol in Ag sol as reported in recent literature, thereby providing direct spectral evidence. Copyright © 2011 John Wiley & Sons, Ltd.     

Measurement of absolute photoluminescence quantum yields using integrating spheres – Which way to go?

Two common methods for recording absolute photoluminescence quantum yields using integrating spheres are discussed. These methods are developed from a theoretical standpoint, with a discussion of the assumptions made in each and their principle differences, and practical comparisons between the two are made using a range of different materials and sample types. It is shown that despite the underlying theoretical differences both methods ultimately yield very similar experimental results. Additionally, the concept of a time‐dependent quantum yield is examined and preliminary studies along these lines are presented in the form of an investigation into the photo‐oxidation of a luminescent polymer film.     

Intra‐ and intermolecular N?H···O hydrogen bonds in pyrrolyl derivatives of indane‐1,3‐dione – experimental and theoretical study

2‐(Pyrrol‐2‐ylmethylene)‐1,3‐indandione ( 4 ) and 2‐(pyrrol‐2‐ylmethylene)‐3‐dicyanomethylidene‐1‐indanone ( 5 ) were synthesized. Multinuclear and 2D‐NMR, IR, UV spectroscopic investigations as well as quantum chemical calculations showed the presence of strong hydrogen bonding in these molecules. For both molecules, the presence of two conformers, with and without H‐bond, was experimentally detected in the basic solvents (DMSO, acetone, pyridine) and the solvate complexes were theoretically calculated. Specific behavior of the intramolecular H‐bonded complexes different from that of the intermolecular H‐complexes is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Computational study of singlet and triplet sulfonylnitrenes insertion into 1,3‐butadienes: 1,2‐ or 1,4‐cycloaddition?

The formation of N‐trifluoromethylsulfonyl‐2‐vinylaziridine and N‐trifluoromethylsulfonyl‐3‐pyrroline by the reaction of the singlet and triplet trifluoromethanesulfonylnitrenes with s‐cis‐ and s‐trans‐1,3‐butadienes was studied theoretically at the B3LYP/6‐311++G(d,p) and M06‐2X/6‐311++G(d,p) levels of theory. The singlet trifluoromethanesulfonylnitrene adds to s‐cis‐ and s‐trans‐1,3‐butadiene exothermally in one step to give the product of 1,2‐cycloaddition, N‐trifluoromethylsulfonyl‐2‐vinylaziridine, the energy decreasing by 88.5 and 86.2 kcal/mol at the B3LYP level and by 105.2 and 103.0 kcal/mol at the M06‐2X level, respectively. The formed 2‐vinylaziridine can undergo rotation about the C(2)–C_sp2 bond with the barrier not exceeding 3.5 kcal/mol and to rearrange into N‐trifluoromethylsulfonyl‐3‐pyrroline. The triplet trifluoromethanesulfonylnitrene reacts with s‐cis‐ and s‐trans‐1,3‐butadiene in two steps. The first exothermic step is the formation of the triplet diradical adducts. The second step is the spin inversion with the energy raising by 5.8 and 17.8 kcal/mol at the B3LYP level and by 11.0 and 20.8 kcal/mol at the M06‐2X level for the adducts to s‐cis‐ and s‐trans‐1,3‐butadiene, respectively. Recombination of the radical centers occurs selectively to give N‐trifluoromethylsulfonyl‐2‐vinylaziridine that is exothermally rearranged into N‐trifluoromethylsulfonyl‐3‐pyrroline with the energy barrier of 40 kcal/mol at the B3LYP level and of 50 kcal/mol at the M06‐2X level. Copyright © 2014 John Wiley & Sons, Ltd.     

Can tetra‐tert‐butylethylene be formed by ion–ion recombination or ion–molecule reaction of two di‐tert‐butylcarbene units?—a DFT study

The reaction channels of di‐tert‐butylcarbene ( 2 ), its radical anion, ( 3 ) and its radical cation ( 4 ) were investigated theoretically by using DFT/B3LYP with 6‐31+G(d) basis set and 6‐311+G(2d,p) for single point energy calculations. Conversion of the neutral carbene 2 to the charged species 3 and 4 results in significant geometric changes. In cation 4 two different types of C? (CH₃)₃ bonds are observed: one elongated sigma bond called “axial” with 1.61 Å and two normal sigma bonds with a bond length of 1.55 Å. Species 2 and 4 have an electron deficient carbon center; therefore, migration of CH₃ and H is observed from adjacent tert‐butyl groups with low activation energies in the range of 6–9 kcal/mol like similar Wagner–Meerwein rearrangements in the neopentyl‐cation system. Neutral carbene 2 shows C? H insertion to give a cyclopropane derivative with an activation energy of 6.1 kcal/mol in agreement with former calculations. Contrary to species 2 and 4 , the radical anion 3 has an electron rich carbon center which results in much higher calculated activation energies of 26.3 and 42.1 kcal/mol for H and CH₃ migrations, respectively. NBO charge distribution indicates that the hydrogen migrates as a proton. The central issue of this work is the question: how can tetra‐tert‐butylethylene ( 1 ) be prepared from reaction of either species 2 , 3 , or 4 as precursors? The ion–ion reaction between 3 and 4 to give alkene 1 with a calculated reaction enthalpy of 203.5 kcal/mol is extremely exothermic. This high energy decomposes alkene 1 after its formation into two molecules of carbene 2 spontaneously. Ion–molecule reaction of radical anion 3 with the neutral carbene 2 is a much better choice: via a proper oriented charge–transfer complex the radical anion of tetra‐tert‐butylethylene (11) is formed. The electron affinity of 1 was calculated to be negligible. Copyright © 2010 John Wiley & Sons, Ltd.     

Why the ΔνCH blue shift is larger in chloral than in dichloroacetyl chloride dimers?

Raman spectra of the Cl₃CCHO/CCl₄ and Cl₃CCHO/C₆D₁₂ binary systems were recorded as a function of the mole fraction. Features originating from self‐aggregates of chloral (trichloroethanal, trichloroacetaldehyde—TCAA) molecules were detected in different spectral regions. The most pronounced changes were observed in the vicinity of the ν(CO) and ν(C H) stretching vibration bands. Using two‐dimensional correlation spectroscopy (2D‐COS), evolving‐factor analysis (EFA) and multivariate curve resolution (MCR), dimer bands were identified, and their positions were determined. The ν(C H) stretching vibration band in dimers was blue‐shifted by nearly 18 cm⁻¹, whereas the ν(CO) dimer band was red‐shifted by more than 5 cm⁻¹. For these bands, the observed shifts were accompanied by an almost twofold change in the bandwidth, from approximately 19 and 6 cm⁻¹ for dilute solutions (x = 0.05) to 36.6 and 11.5 cm⁻¹, respectively, in pure TCAA. The formation of dimers was confirmed by multivariate analysis of the Raman spectra of chloral recorded as a function of temperature. Analogous analysis of dichloroacetyl chloride (DCAC) spectra gave an 8.9 cm⁻¹ blue shift for the ν(C H) vibration band and − 5.5/− 10.1 cm⁻¹ shifts for the ν(CO) stretching vibrations of the two conformers present. To facilitate the interpretation of experimental findings, the optimized geometries and vibrational wavenumbers of the Cl₃CCHO/HCl₂CCClO molecules and (Cl₃CCHO)₂/(HCl₂CCClO)₂ dimers were calculated at the B3LYP/6‐311 + + G(3df,3pd) level. Copyright © 2010 John Wiley & Sons, Ltd.     

Can 2‐acylpyrroles form an intramolecular hydrogen bond?

The formation of intramolecular hydrogen bonding by certain N‐substituted 2‐acylpyrroles has been demonstrated by B3LYP/aug‐cc‐pVDZ calculations, the quantum theory of atoms in molecules, and the natural bond orbital method. Total electron energy densities H_BCP at the bond critical point of the H?O bond were applied to analyze the strength of these interactions. The relations between quantum theory of atoms in molecules, carbonyl stretching vibrational modes ν_{C = O}, and natural bond orbital parameters associated with the formation of the C–H?O interaction have been established. The short contacts were found experimentally in the crystal structure of a new 2‐acylpyrrole derivative 5‐chloro‐2‐oxopentyl‐1‐(5‐chloro‐2‐oxopentyl)pyrrolo‐2‐carboxylate. The influence of 2‐ and N‐substitution of 2‐acylpyrroles on C‐H?O interaction energy is discussed. It was found that the methylene group may act as a proton donor leading to a red‐shift or blue‐shift phenomenon of the ν_C–H stretching mode. Copyright © 2015 John Wiley & Sons, Ltd.     

Which Physical Quantity Deserves the Name “Quantity of Heat”?

“What is heat?” was the title of a 1954 article by Freeman J. Dyson, published in Scientific American. Apparently, it was appropriate to ask this question at that time. The answer is given in the very first sentence of the article: heat is disordered energy. We will ask the same question again, but with a different expectation for its answer. Let us imagine that all the thermodynamic knowledge is already available: both the theory of phenomenological thermodynamics and that of statistical thermodynamics, including quantum statistics, but that the term “heat” has not yet been attributed to any of the variables of the theory. With the question “What is heat?” we now mean: which of the physical quantities deserves this name? There are several candidates: the quantities Q, H, Etherm and S. We can then formulate a desideratum, or a profile: What properties should such a measure of the quantity or amount of heat ideally have? Then, we evaluate all the candidates for their suitability. It turns out that the winner is the quantity S, which we know by the name of entropy. In the second part of the paper, we examine why entropy has not succeeded in establishing itself as a measure for the amount of heat, and we show that there is a real chance today to make up for what was missed.     

Experimental study on the reaction pathway of α‐haloacetophenones with nucleophiles: direct substitution or carbonyl addition?

The reaction of PhCOCH₂Cl with OH^– gave the expected α‐substituted alcohol (PhCOCH₂OH) in addition to three dimer products. To clarify whether the substitution product is formed by direct S_N2 or via carbonyl addition, the reaction of PhCOCH₂Cl and OMe^– was examined. The reaction gave two products, PhCOCH₂OH as the major product after acid hydrolysis and PhCOCH₂OMe as the minor product. An electron‐withdrawing substituent on the phenyl ring enhanced the overall reactivity and gave more alcohol than ether. It was concluded that the alcohol was formed via carbonyl addition‐epoxidation route, whereas the ether was formed by the direct substitution route. Copyright © 2012 John Wiley & Sons, Ltd.     

Where Is a Singer''s Voice if It Is Placed “Forward”?

Singing teachers sometimes characterize voice quality in terms of "forward" and "backward" placement. In view of our traditional knowledge about voice production it is hard to explain any possible acoustic or articulatory differences between the voices so "placed." The analysis of the teachers' expert opinions demonstrates that, in general, a voice placed "forward" indicates a desirable quality that students should attain by the end of their studies. Productions that were perceived as "forward" and "backward" were selected from the listening test. The acoustic analysis of those productions reveals that the voice quality in the case of "forward" placement correlates with higher frequencies of the second (F2) and third (F3) formants, as well as with a more salient "singer's formant" in the voice. The five basic vowels were included in the investigation.     

Assessment of Raman microscopy coupled with principal component analysis to examine egg yolk–pigment interaction based on the protein C?H stretching region (3100–2800 cm−1)

This work seeks to identify the slight changes in the characteristic C H stretching region (3100–2800 cm⁻¹) of a protein‐based binder and fatty acid esters from egg yolk, which may occur in complex paint samples due to the presence of particular pigments. To date, this protein region—where historic pigments do not show characteristic Raman bands—has not been used to identify possible interactions between painting materials, in spite of its potential due to the mentioned feature. This study is based on the investigation of pure egg yolk model samples and tempera model samples prepared by mixing this binder with some historic pigments (cinnabar, raw Sienna, lead white, gypsum, calcite, azurite, lapis lazuli and smalt) as binary samples. All samples were analyzed in this region by Raman microscopy (RM) coupled with principal component analysis (PCA) for three color groups (red, white and blue) separately. The results show relevant spectral changes in the C H stretching region of amino acids and polyunsaturated fatty acids esters of the egg yolk binder, particularly in the azurite, lead white and gypsum‐based tempera samples. Lesser interactions were discerned in the tempera samples made with smalt, as well as shift in the region of polyunsaturated fatty acid esters of the egg yolk binder in the cinnabar and raw Sienna‐based tempera paintings. No interactions were recognized between the egg yolk and the pigments calcite and lapis lazuli. The effectiveness of applying RM combined with PCA for identifying interaction processes between binders and pigments is demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.     

How does the s(E + N) equation work? Comparisons with a modified Swain–Scott equation (E + sN) and revision of the N1 scale of solvent nucleophilicity

Modifications of the Swain–Scott equation (log k/k₀) = sn) give an equation log k₁ = (E + sN₁′); k₁ is the rate constant, E is an electrophilicity parameter, N₁′ is a solvent nucleophilicity parameter and s is an electrophile‐specific sensitivity parameter. The equation is tested using over 300 published first‐order rate constants (k₁) for decay of a range of benzhydrylium cations in various solvents, on which the published N₁ scale of solvent nucleophilicity is based (S. Minegishi, S. Kobayashi and H. Mayr, J. Am. Chem. Soc. 2004, 126, 5174–5181) using the alternative equation log k = s(E + N₁), in which s is a nucleophile‐specific parameter. The modified (E + sN₁′) equation provides a revised N₁′ scale of solvent nucleophilicity, and a more precise fit, with less than half the number of adjustable parameters. It is found that the sensitivities of the benzhydrylium cations to changes in solvent nucleophilicity decrease slightly as reactivity increases, in contrast to s(E + N) equations, which show no trends in s values. It is proposed that more reliable N scales can be defined using (E + sN), because N is determined directly from definitions, and residual errors (e.g. experimental or due to solvation effects) can be incorporated into the slope and intercept. The complex reasons for the success of equations of the type log k = s(E + N) are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Ionized physical vapor deposited Al2O3 films: Does subplantation favor formation of α‐Al2O3?

The broad energy distributions of the condensing particles typically encountered in ion assisted vapor deposition techniques are often a drawback when attempting to understand the effect of the energetic bombardment on the film properties. In the current study, a monoenergetic Al⁺ beam generated by a filtered cathodic arc discharge is employed for the deposition of alumina (Al₂O₃) films at well defined Al⁺ ion energies between 4 eV and 200 eV at a substrate temperature of 720 °C. Structural analysis shows that Al⁺ energies of 40 eV or larger favor the formation of the thermodynamically stable α‐Al₂O₃ phase at the expense of other metastable Al₂O₃ polymorphs. The well defined ion energies are used as input for Monte‐Carlo based simulations of the ion–surface interactions. The results of these simulations reveal that the increase of the Al⁺ ion energy leads to an increase in the fraction of ions subplanted into the growing film. These findings underline the previously not considered role of subsurface processes on the phase formation of ionized physical vapor deposited Al₂O₃ films. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

40 Years of Presentation Particle Size Distributions–Yet Still Incorrect?

While the quality and variety of particle size measuring instruments have improved dramatically in recent years, both in their accuracy and in their speed of measurement, the representation of the measured data – particularly the density distribution – has generally received little attention from the manufacturers. The depiction of a continuous density distribution by a percentage value on the ordinate makes no sense. Although logarithmic density distributions serve a purpose with distinctly separated bi‐ or multimodal distributions (by analogy with analytical chemical spectra), they can lead to serious interpretation errors in the case of the monomodal distribution. Thus for monomodal distributions either the density distribution q_r(x) should be used or no representation of the density distribution attempted.     

Remote substituent effects on homolytic Fe?C bond energies of p‐G‐C6H4CH2Fe(CO)2(η5‐C5H5) and p‐G‐C6H4(H)(CN)CFe(CO)2(η5‐C5H5) studied by Hartree–Fock and density functional theory methods

In general, both stoichiometric and catalytic reactions of organometallic complexes involve breaking and forming metal–ligand bonds. Therefore, an evaluation of the thermodynamics of such reactions requires the knowledge of metal–ligand bond energies (BDEs). The homolytic Fe? C bond dissociation energies [i.e., ΔH_homo(Fe? C)s] of 12 para‐substituted benzyldicarbonyl(η⁵‐cyclopentadienyl)iron, p‐G‐C₆H₄CH₂Fp [1,G = NO₂, CN, COMe, CO₂Me, CF₃, Br, Cl, F, H, Me, MeO, NMe₂; Fp = (η⁵‐C₅H₅)(CO)₂Fe] and 12 para‐substituted α‐cyanobenzyldicarbonyl (η⁵‐cyclopentadienyl)iron, p‐G‐PANFp [2,PAN = C₆H₄CH(CN)] were studied using Hartree–Fock (HF) and density functional theory (DFT) methods with large basis sets. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔH_homo(Fe? C)s. The B3LYP method satisfactorily predicts the α and remote substituent effects on ΔH_homo(Fe? C)s [ΔΔH_homo(Fe? C)s]. The fair correlations [r = 0.97 (g, 1), 0.99(g, 2)] of ΔΔH_homo(Fe? C)s of series 1 and 2 with the substituent σ constants imply that the para substituent effects on ΔH_homo(Fe? C)s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. The molecule stabilization effects (MEs) causes that not only the magnitude of ΔΔH_homo(Fe? C)s(1) varies significantly but also the direction changes from S‐pattern to O‐pattern. ΔΔH_homo(Fe? C)s(2) were found to conform to the Capto‐dative Principle. The detailed knowledge of the factors that determine the Fp? C bond strengths would greatly aid in understanding reactivity patterns in many processes. Copyright © 2010 John Wiley & Sons, Ltd.     

RTP Q-switched 2 μm Tm,Ho:GdVO<Subscript>4</Subscript> Laser

In this paper, we report the performance of a diode-pumped cryogenic Tm (5 at %), Ho (0.5 at %):GdVO₄ laser with an RTP pockel cell Q-switch at different pulse repetition rate including 300 Hz, 500 Hz, 1 kHz, and 10 kHz. At the pump power of 6.96 W, the maximum output of 1.7 mJ with a pulse width of 28 ns was achieved under 300 Hz repetition rate, corresponding to a peak power of 61 kW. To the best of our knowledge, this is the first time that RTP was used as a Q-switch generator in the 2 μm Tm,Ho:GdVO₄ laser.