Field Of Molecular Physics Research Articles

Zeolite ATN: Topological characterization and predictive analysis on potential energies using entropy measures

Zeolites serve as multifunctional microporous materials and have potential applications as catalysts, ion exchangers, and adsorbents. Researchers are interested in the topological characterization of zeolite frameworks due to their complex 3D arrangement of atoms. ATN is one of the variants of zeolite whose building block is arranged in a non-isometric cyclic permutation. The long-range and short-range molecular interactions of the ATN framework are influenced by the geometric arrangement of molecules. In this paper, we have investigated Shannon's information entropy measures of the ATN framework using bond degree and neighborhood degree sum based indices as weights. Further, a predictive analysis with the aid of entropy measures to determine the long-range and short-range potential energies has been implemented. The model proposed in this study can be incorporated into the fields of molecular physics and theoretical chemistry to determine the energy levels of microporous materials. Therefore, the predictive model will make a substantial contribution to QSAR/QSPR modeling.

Pure vibrational state energies and statistical-mechanical models for the reparameterized scarf oscillator

In this work, the reparameterized Scarf II oscillator was employed to describe the internal vibration of diatomic systems. Analytical equations for bound state pure vibrational energies and canonical partition function were obtained. The equations were used to derive statistical-mechanical models for the prediction of molar entropy, enthalpy, Gibbs free energy and constant pressure (isobaric) heat capacity of gaseous substances. The obtained model equations were used to generate numerical data on bound state energy eigenvalues and, to investigate the thermodynamic properties of the ground states chloroborane (BCl), bromine fluoride (BrF), and bromine chloride (BrCl) molecules. With the aid of the expression for molar entropy of the system, average absolute deviations obtained for the molecules are 0.1878%, 0.1267%, and 0.0586% from experimental data. The isobaric heat capacity model yields average absolute deviation of 2.1608%, 1.8601%, and 1.9805%. The results obtained are in good agreement with available literature data on gaseous molecule. The work could be applicable in the fields of molecular physics, chemical physics, solid-state physics and chemical engineering.

Formation of Skills for Solving Professionally Oriented Problems in the Field of Molecular Physics

The article shows how to increase the efficiency of practical training in the training of future specialists in the mining and metallurgical industry through the formation of professionally oriented problems in physics.

Visible light-induced thymine dimerisation based on large localised field gradient by non-uniform optical near-field

The localised excitations of several molecular reactions utilising optical irradiation have been studied in the field of molecular physics. In particular, deoxyribonucleic acid (DNA) strands organise the genetic information of all living matter. Therefore, artificial methods for freely controlling reactions using only light irradiation are highly desirable for reactions of these strands; this in regard with artificial protein synthesis, regional genetic curing, and stochastic analysis of several genetic expressions. Generally, DNA strands have strong absorption features in the deep ultra-violet (DUV) region, which are related to the degradation and reconstruction of the strand bonding structures. However, irradiation by DUV light unavoidably induces unintended molecular reactions which can damage and break the DNA strands. In this paper, we report a photo-induced molecular reaction initiated by the irradiation of DNA strands with visible light. We utilised photo-dissociation from the vibrational levels induced by non-uniform optical near-fields surrounding nanometric Au particles to which DNA strands were attached. The results were experimentally observed by a reduction in the DUV absorbance of the DNA strands during irradiation. There was a much higher yield of molecular reactions than expected due to the absorbance of visible light, and no defects were caused in the DNA strands.

High-temperature ideal-gas partition function of the molecule

The molecular partition functions of even the simplest molecules are uncertain at high temperatures. This paper presents an investigation of the existing discrepancies for the molecular ion. The specific aim, apart from a comparison of various results, is to include all interactions between atoms in the molecular partition function to obtain those values which can be called the ideal-gas partition function. A classical mechanics-based method is used, and to extend the results to temperatures below 7000 K the Wigner–Kirkwood quantum correction is applied. Analysis of the results of this paper and others shows significant differences from the results currently known in the field of molecular physics and those used in the field of astrophysics.

An analytic algebraic approach to study the influence of molecular alignment and orientation on multiphoton excitation in intense laser fields

The influence of molecular alignment and orientation on multiphoton vibrational excitation of diatomic molecules H2, HD, and D2 is studied by an analytical algebraic approach. The explicit expressions of the time-evolution operator and the excitation probability are given. The long-time average absorbed energy spectra and the time-dependent absorbed energy are obtained. Results show that the impact of molecular orientation on the multiphoton resonant excitation is decided by the molecular type and molecular anharmonicity. This is valuable for controlling the vibrational excitation of molecules, which is relevant to the whole field of molecular physics and physical chemistry. Furthermore, good agreement with numerical simulation is achieved.

Stanisław Kielich – A personal memoir

In the 1950s I became interested in the interaction of electric fields with gases and liquids. Professor Arkadiusz Piekara was performing pioneering experiments in Poznan on dielectric saturation. He had discovered “the inverse saturation effect” in which the permittivity of dipolar liquids like nitrobenzene increased in strong applied electric fields; he correctly interpreted this effect in terms of the favouring of the more dipolar configurations of clusters of molecules by the applied field. I was invited to visit Poznan in April 1959 and there met Stanislaw Kielich, Professor Piekara’s outstanding young colleague. I particularly admired the close interaction of theory and experiment that was a feature of the Instytut Fiziki in Poznan. Kielich was four years my senior and his interests closely overlapped my own in optical, electric and magnetic properties of matter and in intermolecular forces We had many conversations and I remember his excitement on hearing about a new method of measuring molecular quadrupole moments. Poland was a poor country at that time but I was very generously and graciously entertained and had the pleasure of dancing with Stanislaw’s delightful wife Clare. When I departed from Poznan on the train for Warsaw he presented me with a paper knife bearing the arms of the city. It has been on my desk ever since. Kielich went on to become a leader in various fields of molecular physics, and particularly in non-linear phenomena. He enjoyed the respect and affection of colleagues around the world and brought great credit to the Adam Mickiewicz University and to Poland. I am grateful for this opportunity to pay tribute to a friend and distinguished colleague.

Laser-Intensity Dependent Vibrational Excitation and Alignment of Molecular Ions in the Ultrafast Multiphoton Regime

H2 molecules were ionized in the ultrafast (approximately 150 fs) multiphoton regime (263 nm, approximately 10(13) W cm(-2)). Earlier experiments investigated the kinetic energies of electrons or ions only. Using a unique experiment, we show that the vibrational excitation of molecular ions contains essential information about the dynamics of the process. In addition, we prove some earlier interpretations wrong. A realistic model based on vibronically excited intermediates, Stark shifting into resonance, reproduces the measurements, demonstrating that resonances continue to be important in the femtosecond regime. This eventually enables ultrafast control of the vibrational excitation of molecular ions, which is relevant to the whole field of molecular physics and physical chemistry.

Discovery of the Double Exponential Transformation and Its Developments

This article is mainly concerned how the double exponential formula for numerical integration was discovered and how it has been developed thereafter. For evaluation of I = \int_{-1}^1 f(x)dx , H. Takahasi and M. Mori took advantage of the optimality of the trapezoidal formula over (−∞, ∞) with an equal mesh size and proposed in 1974 x = \phi(t) = \tanh(\frac{π}{2} \sinh t) as an optimal choice of variable transformation which transforms the original integral to I = \int^∞_{−∞} f(\phi(t))\phi' (t) dt . If the trapezoidal formula is applied to the transformed integral and the resulting infinite summation is properly truncated a quadrature formula I ≈ h ∑^n_{k=−n}f_(\phi(kh))\phi'(kh) is obtained. Its error is expressed as O(\exp(−CN/ \log\, N_)) as a function of the number N ( = 2n + 1 ) of function evaluations. Since the integrand decays double exponentially after the transformation it is called the double exponential (DE) formula. It is also shown that the formula is optimal in the sense that there is no quadrature formula obtained by variable transformation whose error decays faster than O(\exp(−CN/ \log\, N)) as N becomes large. Since the paper by Takahasi and Mori was published the DE formula has gradually come to be used widely in various fields of science and engineering. In fact we can find papers in which the DE formula is successfully used in the fields of molecular physics, fluid dynamics, statistics, civil engineering, financial engineering, in particular in the field of the boundary element method, and so on. The DE transformation has turned out to be also useful for evaluation of indefinite integrals, for solution of integral equations and for solution of ordinary differential equations, so that the scope of its applications is expected to spread also in the future.

Molecular parity violation in electronically excited states

One of the greatest challenges in the field of molecular physics is the still outstanding measurement of the parity violating energy difference (ΔEpv) which electroweak theory predicts to exist between the enantiomers of chiral molecules. Apparently, previous attempts to detect signals of parity violation in molecules almost exclusively focused on electronic ground state systems. But as this study reveals, there are good reasons to believe that compounds which are chiral in an electronically excited state are particularly suited for a possible proof of molecular parity violation. Here, first calculations of the parity violating energy difference in electronically excited states are presented and routes to its measurement are discussed.

On the application of canonical perturbation theory to floppy molecules

Canonical perturbation theory (CPT) is a powerful tool in the field of molecular physics. It consists of a series of coordinate transformations aimed at rewriting the Hamiltonian in a simpler form without modifying the geometry of the phase space. The major achievement of CPT is the straightforward derivation of relations between the physically meaningful parameters of potential energy surfaces and the coefficients of the so-called effective Hamiltonians. While most of the studies performed up to date deal with surfaces expanded in polynomial series around a single minimum, CPT has also been applied to mixed polynomial/trigonometric expansions in the treatment of torsions. In this latter case, however, the accuracy of CPT has not been verified. The goal of this article is to suggest some modifications of the procedures, which allow for the successful application of CPT to floppy molecules with several equilibrium positions and nonpolynomial expansions. The levels belonging to all the wells or located above the saddle points are satisfactorily reproduced by the perturbative Hamiltonian. More precisely, the vibrational modes are sorted into two categories, namely oscillator-like ones and hindered-rotor-like ones. The application of CPT enables the expression of the Hamiltonian in terms of the good quantum numbers and/or classical constants of the motion associated with the oscillator-like modes. The perturbative Hamiltonian then acts on the reduced dimensional space of the hindered-rotor-like modes. The validity and accuracy of this approach are tested on two-dimensional and three-dimensional models mimicking, respectively, nonlinear and linear HCN.

On the Hartree-Fock approximation to the electronic structure of molecule in the intense radiation field and the strong vibronic coupling

The Hartree-Fock approximation has been generalized to incorporate the nonadiabatic effect of molecular vibration previously by Tachibana et al. Here, we will derive the Hartree-Fock equation which reflects also the nonlinear effect of the infrared radiation field as well by using the Bloch-Nordsieck transformation which was discussed first by Nguyen-Dang and Bandrauk in the field of molecular physics. The Hartree-Fock equation reflects the non-adiabatic coupling between an electron and a molecular vibration and between the electron and a infrared radiation fields. The infrared radiation field also affects the dynamics of nuclear motion.

Coefficients of interest for molecular spectroscopy

Some basic considerations on the coupling coefficients for a chain of molecular groups starting from the natural universal covering SU 2 of the proper rotation group SO 3 are reviewed. Special emphasis is placed on the so-called f coefficients. Similar coefficients introduced by various people working in the field of molecular physics are related to the f and associated coefficients. The f coefficients are useful in different branches of molecular spectroscopy. Some specific applications to the ligand field theory are discussed in detail.

Prof. J. E. Lennard-Jones

THE first occupant of the recently created John Humphrey Plummer chair of inorganic chemistry at Cambridge will be Prof. J. E. Lennard-Jones, of the University of Bristol. During his tenure of office at Bristol, first as reader in theoretical physics and later as professor and first holder of the Melville Wills chair in this subject in the Wills Physical Laboratory, Prof. Lennard-Jones has carried out a number of important investigations in the field of molecular physics. His earlier work on the forces between atoms in gases, and later, in crystals, was of fundamental importance and led him to the study of cohesion and other surface phenomena such as adsorption, as well as the structure of molecules in general. The results that he obtained attracted general attention and were particularly appreciated by physical chemists and metallurgists, both in Great Britain and abroad, because of the light that was thereby thrown upon some of the most fundamental problems of modern chemistry. The post to which Prof. Lennard-Jones has now been appointed affords special opportunities for the continuation of this co-operation between theoretical physicists and chemists, which in the past has been far less marked in Great Britain than on the Continent. On the other hand, the University of Bristol, with which he has been associated for seven years, suffers the loss of an original thinker, a brilliant expositor, and a capable administrator.