Failures of Classical Physics Revisited, and Understood

The effect of spectral line shape on apparent rotational temperatures of OH has been investigated for the P1 branch, 2Σ→2Π transitions, (0, 0) band, by treating the ratio of collision half-width to Doppler half-width as a variable parameter. The results of calculations for emission experiments, using conventional plots, show a large effect of line shape on apparent temperature. In general, the greater the ratio of collision half-width to Doppler half-width, the smaller the distortion of experimental data. The analysis predicts higher apparent rotational temperatures for isothermal systems at reduced pressures than at atmospheric pressures. Although this result is in agreement with experimental observations on flames, it cannot be used as an explanation for the observed data without auxiliary studies proving that distortion of data is of importance in any given case. The two-path method for determining temperatures and emissivities (concentrations) in flames has been extended to spectral lines with combined Doppler- and collision-broadening.

In high-throughput proteomics the development of computational methods and novel experimental strategies often rely on each other. In certain areas, mass spectrometry methods for data acquisition are ahead of computational methods to interpret the resulting tandem mass spectra. Particularly, although there are numerous situations in which a mixture tandem mass spectrum can contain fragment ions from two or more peptides, nearly all database search tools still make the assumption that each tandem mass spectrum comes from one peptide. Common examples include mixture spectra from co-eluting peptides in complex samples, spectra generated from data-independent acquisition methods, and spectra from peptides with complex post-translational modifications. We propose a new database search tool (MixDB) that is able to identify mixture tandem mass spectra from more than one peptide. We show that peptides can be reliably identified with up to 95% accuracy from mixture spectra while considering only a 0.01% of all possible peptide pairs (four orders of magnitude speedup). Comparison with current database search methods indicates that our approach has better or comparable sensitivity and precision at identifying single-peptide spectra while simultaneously being able to identify 38% more peptides from mixture spectra at significantly higher precision.

Stochastic modelling of relaxation effects in line shapes

Final-state correlation effects in Auger line shapes are considered within the cluster linear combination of atomic orbitals-molecular orbitals-configuration interaction theory with a parametrized Hamiltonian. A model problem is solved analytically to elucidate the role of final-state hole-hole correlation and to understand the localization of the holes on rather small subclusters of the system. The relationship of the correlation effects to the relative magnitudes of the one-center hole-hole repulsion $u$ and the bandwidth $\ensuremath{\Gamma}$ has been previously reported; however, this previous work has been limited to metallic single element conductors. This work extends the theory to covalently bonded insulators (and possibly semiconductors) consisting of more than one element. Application of the theory is made to the O $\mathrm{KVV}$ and Si ${L}_{23}\mathrm{VV}$ Auger line shapes from Si${\mathrm{O}}_{2}$. A high-energy shoulder at 511 eV in the O $\mathrm{KVV}$ line shape is interpreted as arising directly from correlation effects. A peak at 50 eV in the Si ${L}_{23}\mathrm{VV}$ line shape, its intensity significantly underestimated by the previous theory, is now accounted for; a peak at 70 eV previously suggested to be a shake satellite is now indicated also to arise from correlation effects. Both line shapes reveal a density of states primarily localized on an ${\mathrm{Si}}_{2}$O subcluster. The magnitude of the hole-hole repulsion on the subcluster and between neighboring ${\mathrm{Si}}_{2}$O subclusters is empirically determined from the Auger line shapes to be \ensuremath{\sim} 11 and 4 eV, respectively. The oxygen $2p$ nonbonding bandwidth is estimated to be \ensuremath{\sim} 6 eV, but in light of other theoretical and experimental results, our result is believed to be 1-2 eV too large. Reasons for our overestimate are discussed.

Stereoselectivity or stereorequirement refers to the enhancement of chemical reactivity resulting from the preferential alignment/orientation of the colliding reactants. This concept is deeply embodied in the pre-exponential A-factor of the Arrhenius rate expression or the entropy effect of thermal kinetics in physical chemistry textbooks. To understand its dynamical consequence and seek for its mechanistic origin, two different approaches of either selecting the rotational states of the reactant or aligning/orienting the reactant in the laboratory have traditionally been taken. Due to the experimental challenges, theory is far more advanced than experiment. However, even for the simple atom + diatom reaction, the physical interpretations of the calculated results can sometimes be ambiguous or controversial because of the entangled potential and kinematic factors. In this Feature Article, we try to experimentally tackle the problem for reactions with polyatomic reactants by adopting both approaches in parallel for the same reaction. By comparing the results from the two approaches as well as contrasting them with the analogous reactants-here, a symmetric-top CHD3 versus a spherical-top CH4, deeper physical insights are gained, which paves the road for future studies of complex systems and for establishing a more complete conceptual framework.

Taking chemical potential as the main line, this paper mainly introduces the derivation of various types of chemical reaction isotherms both systematically and completely in physical chemistry textbooks. By doing so, on the one hand, it can further consolidate and strengthen the students' understanding and application of the chemical potentials of different kinds of substances. On the other hand, it can also make clear the origin of various types of chemical reaction isotherms rather directly and be helpful to the students for their correct understanding and calculation of standard molar Gibbs free energy change G  r m Δ , standard equilibrium constant K  (also named thermodynamic equilibrium constant) and reaction quotient Q of various types of chemical reactions. Hence, a rather good teaching effectiveness can be achieved hopefully.

The authors analyze the role of the 4π factor and to show the equivalence of two formulas that are most commonly used in physical chemistry textbooks.

The effect of the spin packet lineshape on the saturation of inhomogeneous resonances

Enhanced capability to collect hypersonic flight data is required to better understand the flow physics around spacecraft entering Earth’s atmosphere. Especially daytime recording, while possible, is challenging, requiring compromises due to saturation and environmental noise. Using event-based cameras will allow spectral measurements to be done equally well during the day and night without modifications to instrumentation, overcoming the current major limitation associated with daytime tests. Combining these cameras with high-resolution spectroscopy enables more reliable collection of critical data, such as the flow temperature and species composition. Measurements were performed using a novel neuromorphic spectroscopy system and a range of light sources, obtaining both broadband and discrete line spectra. Dynamic range and long-range spectroscopy results show performance improvement of the event-based system over the camera typically used for the conditions tested, first-time demonstrating that neuromorphic spectroscopy systems are capable of successfully recording emission spectra.

The interaction of strongly adsorbed oxygen with free spin centers in carbon

Aggregation-induced emission (AIE) spectra accompanied by excited state intramolecular proton transfer (ESIPT) for two triphenylamine salicylaldehyde derivatives (namely, TS and TS-OMe) are investigated by performing molecular spectral and dynamics simulations associated with the hybrid quantum mechanics/molecular mechanics (QM/MM) at the quantum level of the time-dependent density functional theory. The simulated emission spectral peaks and Stokes' shifts are in good agreement with the experimental results for both TS and TS-OMe. Furthermore, the AIE spectral mechanisms are well explained to be associated with the ESIPT processes for both TS and TS-OMe monomers in the aggregated crystal state, while the AIE spectra mechanism for the TS-OMe (TS) dimer is accompanied by intermolecular charge-transfer excitation process. Besides, the TS dimers also contributed to the AIE mechanisms in the crystal with the intermolecular charge-transfer from one monomer to another. In addition, the TS dimers are contributed to the AIE mechanisms in the crystal with the intermolecular charge-transfer from one monomer to another. On the other hand, simulated emission spectra for both the TS and TS-OMe monomers in acetonitrile solution are involved in mixed emission with and without the ESIPT process, as interpreted by nonadiabatic molecular dynamics simulation. It is also briefly addressed that the emission spectra in the solution are weak and enhanced in the crystal. The present study provides a great physical insight into the design of highly efficient AIE compounds.

Chemical bond plays a central role in the description of the physicochemical properties of molecules and solids and it is essential to several fields in science and engineering, governing the material’s mechanical, electrical, catalytic and optoelectronic properties, among others. Due to this indisputable importance, a proper description of chemical bond is needed, commonly obtained through solving the Schrödinger equation of the system with either molecular orbital theory (molecules) or band theory (solids). However, connecting these seemingly different concepts is not a straightforward task for students and there is a gap in the available textbooks concerning this subject. This work presents a chemical content to be added in the physical chemistry undergraduate courses, in which the framework of molecular orbitals was used to qualitatively explain the standard state of the chemical elements and some properties of the resulting material, such as gas or crystalline solids. Here in Part 1, we were able to show the transition from Van der Waals clusters to metal in alkali and alkaline earth systems. In Part 2 and 3 of this three-part work, the present framework is applied to main group elements and transition metals. The original content discussed here can be adapted and incorporated in undergraduate and graduate physical chemistry and/or materials science textbooks and also serves as a conceptual guide to subsequent disciplines such as quantum chemistry, quantum mechanics and solid-state physics.

The A 2Π–X 2Σ+ band (the Δv = 0 sequence) emission of beryllium deuteride (BeD) molecules has been observed both in Be-seeded deuterium plasma and in front of Be targets exposed to deuterium plasma. The particle interchange reaction, Be+ + D2 → BeD + D+, is thought to be a dominant process for the BeD formation in the plasma. On the other hand, BeD observed in front of Be targets is a product of chemical sputtering of Be bombarded by deuterium plasma. The photon emission coefficient of the A–X band at λ ∼ 497.3–499.2 nm around the prominent Q branch is estimated to be ∼5 × 10−14 m3 s−1 for electron temperatures ≳8 eV as deduced from particle balance between Be, Be+, and BeD in D2 neutral pressure scans. The surface temperature dependence of chemical sputtering of Be released as BeD is investigated, and the sputtering yield of BeD is found to peak at ∼440 K. This peak temperature is consistent with the onset temperature of the decomposition of BeD2, obtained from thermal desorption spectrometry of BeD2 powder. Also, the chemical sputtering yield is observed to be decreased with increasing incident ion flux, similar to carbon. Vibrational (Tvib) and rotational (Trot) temperatures of BeD molecules are evaluated by fitting a measured A–X band spectrum with a simulated spectrum. Spectra taken from BeD formed in the plasma are well fitted with a single pair of Tvib and Trot, which increase linearly with electron density. However, the vibrational and rotational energy of sputtered BeD is found not to be consistent with a Boltzmann distribution.

Calculation and simulation of spectroscopic properties for rare earth ions in chloro-fluorozirconate glasses

In this paper we report precision studies of I₂¹²⁷ hyperfine structure using laser molecular-beam techniques. A single-frequency 5145 Å argon laser tunable over 0.1 Å was used to excite a molecular beam of 12 at right angles. The induced fluorescence was collected by a lens system and focused onto a photomultiplier. The I₂ transitions excited were the hyperfine compo-nents of the P(13) and R(15), 43-0 lines between the z, and 31-1 electronic states. go u The hyperfine frequency spacings were precisely determined by counting the beat frequency between two lasers that were long-term stabilized to various hyperfine lines. The standard deviation of the measurements was approximately 25 kHz. The measured spectrum was fitted to obtain a quadrupole coupling strength difference AeQq= 1894.48 . 36 MHz and a spin-rotation interaction strength difference AC, = 190.7 ± 1.5 kHz between the upper and lower levels of the P(13) transition. For the R(15) transition, we obtained AeQq = 1894. 66 ± .40 MHz and ACI = 187.1 ± 2. 0 kHz. High-resolution line - shape studies were performed using a long-term stabilized laser and an acousto-optic tuning method. The measured width of the individual I₂ transi-tions was 140 kHz (FWHM). By taking into account broadening from the geometric Doppler width, laser jitter, and other small effects, an estimate of 70 kHz (FWHM) for the natural linewidth was obtained which was in excellent agreement with lifetime mea-surements. Attempts to fit the observed line shapes showed clear Lorentzian features. Taking account of the natural linewidth, the instrumental resolution was ≈70 kHz or one part in 10¹⁰.