Independent linear combinations of spectroscopic constants for axially symmetric molecules

The problems of indeterminacy and correlation of spectroscopic constants of axially symmetric molecules are discussed in the dependence on the selection rules of the data set used in analysis of high resolution infrared spectra. Derivation of independent linear combinations of the correlated spectroscopic parameters, for several cases of the allowed and forbidden bands, is carried out for the most important molecular point groups, up to the third order theory. The significance of the forbidden, overtone and hot band transitions in the separate determination of individual constants is also evaluated.     

Prediction of spectroscopic constants for diatomic molecules in the ground and excited states using time-dependent density functional theory

Spectroscopic constants of the ground and next seven low-lying excited states of diatomic molecules CO, N2, P2, and ScF were computed using the density functional theory SAOP/ATZP model, in conjunction with time-dependent density functional theory (TD-DFT) and a recently developed Slater type basis set, ATZP. Spectroscopic constants, including the equilibrium distances r(e), harmonic vibrational frequency omega(e), vibrational anharmonicity omega(e)x(e), rotational constant B(e), centrifugal distortion constant D(e), the vibration-rotation interaction constant alpha(e), and the vibrational zero-point energy E(n)0 were generated in an effort to establish a reliable database for electron spectroscopy. By comparison with experimental values and a similar model with an established larger Slater-type basis set, et-QZ3P-xD, it was found that this model provides reliably accurate results at reduced computational costs, for both the ground and excited states of the molecules. The over all errors of all eight lowest lying electronic states of the molecules under study using the effective basis set are r(e)(+/-4%), omega(e)(+/-5% mostly without exceeding +/-20%), omega(e)x(e)(+/-5% mostly without exceeding 20%, much more accurate than a previous study on this constant of +/-30%), B(e)(+/-8%), D(e)(+/-10%), alpha(e)(+/-10%), and E(n)0(+/-10%). The accuracy obtained using the ATZP basis set is very competitive to the larger et-QZ3P-xD basis set in particular in the ground electronic states. The overall errors in r(e), omega(e)x(e), and alpha(e) in the ground states were given by +/-0.7, +/-10.1, and +/-8.4%, respectively, using the efficient ATZP basis set, which is competitive to the errors of +/-0.5, +/-9.2, and +/-9.1%, respectively for those constants using the larger et-QZ3P-xD basis set. The latter basis set, however, needs approximately four times of the CPU time on the National Supercomputing Facilities (Australia). Due to the efficiency of the model (TD-DFT, SAOP and ATZP), it will be readily applied to study larger molecular systems.     

Calculation of Verdet constants with time-dependent density functional theory: implementation and results for small molecules

We report the implementation of a method by which to calculate Verdet constants for molecules. The method is based on gauge-including atomic orbitals (GIAOs) and density functional theory. Calculations based on this method afford magneto-optical rotations of the right magnitude for the molecules H2, N2, CO, HF, CH4, C2H2, H2O, and CS2. The results are in satisfactory agreement with experiment. We investigate the dependency of the results on the gauge origin if GIAOs are not chosen, the convergence of the results with the size of the basis set for AOs and GIAOs, and for H2O and CS2 a comparison of gas-phase and liquid phase values. For the small molecules studied here, large polarized basis sets with diffuse functions are required to obtain well converged results. The use of an asymptotically correct Kohn-Sham potential is advantageous.     

Polarization propagator calculation of spectroscopic properties of molecules

We propose 10 desirable features or criteria for general purpose methods to be applied to the calculation of a range of spectroscopic properties. We discuss the second-order polarization propagator approximation (SOPPA ) in light of these criteria by giving the actual computational expression used as well as a few numerical examples taken from the theory of NMR spectra (magnetic shieldings and spin-spin coupling constants). We demonstrate that SOPPA comes close to fulfilling these criteria.     

Calculation of spectroscopic constants for the ground electronic states of CsK, CsLi, and RbLi molecules

Vibrational, rotational, and centrifugal constants are calculated for the ground electronic states of CsK, CsLi, and RbLi molecules. This calculation is performed on the basis of potential curves constructed in this work in a wide range of internuclear distances.     

On spectroscopic properties and isotope effects of vibrationally stabilized molecules

Results of quantum and semiclassical calculations obtained for two different potential-energy surfaces are used to discuss spectroscopic properties and isotope effects of the linear IHI and IDI molecules. The potentials are a purely repulsive LEPS surface and a DIM-3C potential with two van der Waals type minima for equivalent IH ··· I and I ··· HI configurations. Both systems are dominated by the effect of vibrational bonding giving rise to some very unusual spectroscopic phenomena, which are discussed in detail. The different vibrational frequencies and rotational constants are roughly estimated as ν₁ = 120 (100) cm^?1, ν₂ = 280 (210) cm^?1, ν₃ = 360 (160) cm^?1 and B = 0.0194 (0.0196) cm^?1 for IHI (IDI). A detailed discussion of the dependence of ν₁, ν₂ and B on ν₃, their sensitivity to variations of the potential-energy surface, and a comparison with the vibrational frequencies of I₂ and HI (ID) is given. It is predicted that there exists only one excited level of the antisymmetric stretching mode. The numbers of symmetrical stretching and bending levels are fairly constant or may even decrease upon deuteration. Simultaneously deuteration destabilizes the molecule. These unusual phenomena are rationalized by our calculations. A set of criteria for observing infrared and Raman bound-to-bound and bound-to-resonance state transitions are presented for the IHI and IDI molecule.     

Dynamics of small,floppy molecules studied by high-resolution spectroscopic techniques

In molecular spectroscopy one of the common interests is how to transform the information obtained by high-resolution spectroscopic techniques into some reliable approximation of the potential energy surface of a particular molecule. Traditionally vibrational spectroscopy has been used. Rotational spectroscopy can only probe, at least at room temperature, molecular transitions arising from excited vibrational states up to approximately 1000 cm^?1. This corresponds roughly to 10% of a typical bond dissociation energy. However, floppy molecules which exhibit a large-amplitude, low-lying vibrational mode can be studied to a large extent by rotational spectroscopy in the microwave, millimeter and submillimeter wave range. Quasilinearity is a special form of large-amplitude motion, which complicates the observed molecular spectra substantially and which presents a real challenge to theoretical spectroscopists. In this lecture the highlights of quasilinear behavior of the molecules HCNO, OCCCO, HNCS and HNCO will be discussed. Another form of large amplitude motion is the inversion exhibited primarily by molecules derived from NH₃. Isocyanamide will be discussed and its special spectroscopic features will be shown. Cyanamide and isocyanamide are potential prebiotic molecules: cyanamide has been detected as a constituent in the interstellar medium. The analysis of the molecular dynamics of these molecules is shown to be necessary for understanding the frequencies and intensities of the observed spectra in the laboratory and in interstellar space.     

Constrained force constants for octahedral molecules

A set of constrained force constants has been derived from experimental vibrational frequency data for eighty three octahedral molecules. Superimposing the condition that the larger value for f_d—f_dd′ be used when f_dα—f_dα″ is a maximum on the six equations relating vibrational frequencies to force constants generates a seventh. This provides a uniform set of results for all 83 molecules. The values of the force constants have a simple rationale in terms of chemical bonding theory. Some preliminary calculations for SF₆ show that these force constants are suitable for use in generating reliable molecular dynamical trajectory data.     

Comparisons between experimental and calculated rate constants for dissociation and combination reactions involving small polyatomic molecules

The experimental results on decomposition and combination reactions involving O₃, HNO₃, NH₃, C₂N₂, and NO₂Cl over extended temperature and pressure ranges are compared with the deductions from RRKM calculations. Quantitative fits of the data over the entire range are possible only if the external (overall) rotations are assumed to be involved in the reactions. Recommended rate constants for the reactions O + O₂ + N₂ → O₃ + N₂ and OH + NO₂ + N₂ → HNO₃ + N₂ are presented.     

Self-consistent molecular hartree—fock—slater calculations. IV. On electron densities,spectroscopic constants and proton affinities of some small molecules

The use of the Xα exchange approximation in calculations on small molecules is studied. Electron densities are very similar to Hartree—Fock densities, as judged from density difference maps. The statistical total energy, E_Xα, is used in order to calculate R_eB_e, ω₃ and D_e of a series of diatomic molecules. The agreement with experiment is again similar to that in Hartree—Fock calculations. Proton affinities can also be calculated very well. The Hartree—Fock—Slater and Hartree—Fock models show on the whole very analogous behaviour. These results are obtained by using accurate, unapproximated, potentials and densities.     

Effect of perturbation of the atomic basis on nuclear magnetic shielding constants for small molecules

We have calculated the components of the paramagnetic part of the magnetic shielding tensor for nuclei in molecules of LiH, HF, and H₂O within the uncoupled variant of Hartree-Fock-Roothaan perturbation theory, taking into account the dependence of the original basis set of Slater-type AO's (STO's) on the perturbation parameter. We have shown that it is necessary to take into account such a dependence when calculating the components of the magnetic shielding tensor in minimal basis sets of STO's. We have carried out a comparative analysis of the data obtained with results of other approaches.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 527–532, September–October, 1988     

Transport properties of small molecules in zwitterionic polymers

Despite great interests in using zwitterionic polymers for membrane surface modification to enhance antifouling properties, there lacks fundamental understanding of the relationship between polymer structure and water/salt separation properties. In this study, two series of zwitterionic polymers were prepared from sulfobetaine methacrylate and 2‐methacryloyloxyethyl phosphorylcholine. Both are crosslinked by poly(ethylene glycol) diacrylate (PEGDA). These copolymers were thoroughly characterized in terms of sol‐gel fraction, density, glass transition temperature, contact angle, water and salt transport properties, and pure‐gas permeability. Interestingly, the zwitterionic polymers exhibit water sorption and permeability similar to noncharged poly(ethylene glycol)‐based materials. These zwitterionic polymers exhibit lower NaCl diffusivity and permeability and thus higher water/NaCl selectivity than the non‐charged PEG‐based materials at similar water volume fractions, demonstrating their promise for membrane surface modification for desalination and wastewater treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1924–1934     

Basis set convergence of indirect spin-spin coupling constants in the Kohn-Sham limit for several small molecules

The performance of more than 40 density functionals in predicting indirect spin-spin coupling constants (SSCCs) in the Kohn-Sham basis set limit was tested. For comparison, similar calculations were performed using the RHF, SOPPA, SOPPA(CC2), and SOPPA(CCSD) methods, and the results were estimated toward the complete basis set (CBS) limit. The SSCCs of nine small molecules (N(2), CO, CO(2), NH(3), CH(4), C(2)H(2), C(2)H(4), C(2)H(6), and C(6)H(6)) were calculated using the dedicated Jensen pcJ-n polarization-consistent basis sets and used for the CBS limit estimations within the Kohn-Sham limit. These CBS results were compared with calculations using the aug-cc-pVTZ-J basis set. Among the 41 studied DFT methods, the tHCTHhyb, HSEh1PBE, HSE2PBE, wB97XD, wB97, and wB97X functionals reproduced accurately the experimental (1)J(XH) SSCCs and (3)J(HH60) and (2)J(HH(gem)) in ethane. Similarly, the functionals HSEh1PBE, HSE2PBE, wB97XD, wB97, and wB97X predicted accurately (1)J(CC), and B98, B97-1, B97-2, PBE1PBE, B1LYP, and O3LYP provided accurate (1)J(CO) results in the CO molecule. A very good performance for the calculation of the SSCCs based on the use of the relatively small basis set aug-cc-pVTZ-J was observed.     

Infrared spectroscopic properties of water molecules dissolved in some oxygen bases

The infrared spectra in the OH-stretching and HOH-bending regions of H₂O, and in the OH-stretching region of HDO dissolved in a number of ketones and ethers have been recorded. The number of component bands and their wavenumbers, halfwidths and intensities, as well as the total OH-stretching intensity in each solvent, have been interpreted in terms of a model for the types of hydrogen bonded solvent:water complexes formed in these systems.The effect of temperature on the spectra of H₂O in some of the ketones has been rationalized on the basis of the equilibrium existing between the different hydrogen bonded species present in solution.     

Universal scaling features of spectroscopic constants for diatomic systems

Based on a new criterion that was proposed to search for the universality of spectroscopic constants for bound ground-state diatomics [R. H. Xie and P. S. Hsu, Phys. Rev. Lett. 96, 243201 (2006)], we have found universal scaling relations between spectroscopic constants of diatomic systems with s-, p-, and d-type valence-shell constituents. Our study suggests a useful empirical approach for the prediction of molecular spectroscopic constants.     

Compensating for variation in 1JCH coupling constants in HSQC spectra acquired on small organic molecules

The HSQC sequence provides a sensitive way of determining the ¹³C chemical shift of protonated carbons. It uses INEPT elements for magnetization transfer, which can only be optimized for one value of ¹J_CH, but small organic molecules contain a wide range of ¹J_CH values. One popular method of compensating for ¹J_CH variation is to incorporate adiabatic pulses into the INEPT elements. This article shows that this method fails for a significant subset of functional groups. It also shows that the effects of this failure can be reduced by avoiding refocusing delays and by using a J‐compensated excitation element. Copyright © 2010 John Wiley & Sons, Ltd.     

Comments on adiabatic calculations of the electrical properties of molecules

The Hamiltonian used in recent calculations (by Silverman, Bishop and others) of the electrical properties of one-electron diatomic molecules is compared, in the adiabatic approximation, with the Stark Hamiltonian.     

From uncharged to decacationic molecules: syntheses and spectroscopic properties of heteroarenium-substituted pyridines

Nucleophilic substitutions on pentachloropyridine with 4-(dimethylamino)pyridine, 4-aminopyridine, and 4-(pyrrolidin-1-yl)pyridine give mono-, tri- and pentacationic pyridine-hetarenium salts. The mono-, tri- and pentacationic 4-aminopyridine derivatives can be deprotonated to neutral compounds in solution, or protonated to di-, hexa- and decacationic pyridine derivatives, respectively. Successive substitutions with different heteroaromatic nucleophiles give pyridines with two distinct types of heteroarenium substituents.