Theoretical Predictions Of Properties Research Articles

Theoretical predictions of properties and adsorption behaviour of a superheavy element Ts and its lighter homolog At, and of their various gas-phase compounds, on hydroxylated quartz surfaces from periodic DFT calculations

Adsorption energies, E ads, of a superheavy element Ts and its lighter homolog At, as well as of their various oxides, hydrides, and (oxy)hydroxides on hydroxylated quartz surfaces are calculated using a periodic density functional theory implemented in the AMS BAND software. It was shown that elemental At and Ts should be the most volatile over the quartz surfaces out of all the considered species, with E ads of the order of van der Waals bond energies, ∼25 kJ/mol. Hydride and hydroxide of At and Ts should be slightly less volatile than the elements with ∼20 kJ/mol larger E ads values. Oxides and oxyhydroxides of these elements should be the least volatile. All the compounds of Ts should be less volatile than the respective At ones. The differences in the E ads values between the Ts species should also be larger than those between the related At compounds, so that one should be able to differentiate between them more easily.

Theoretical predictions of properties and adsorption behaviour of group 1 and 2 elements, including elements 119 and 120, on hydroxylated quartz surfaces from periodic DFT calculations

Adsorption properties of group 1 and 2 elements Cs, Fr and E119 and Ba, Sr and E120, respectively, and of group 1 hydrides and hydroxides on hydroxylated quartz surfaces were calculated using a periodic relativistic DFT approach. The results show that all the considered group 1 and 2 elements should adsorb rather moderately on the quartz surfaces, with E119 and E120 most weakly, due to the strong relativistic stabilisation and contraction of the 8s atomic orbital. This means that E119 and E120 should have a deposition peak in the quartz chromatography column with a temperature gradient from room temperature to far below zero in the sequence Cs/Ba > Fr/Ra > E119/E120. For group 1 element MH and MOH, the adsorption energies are high, so that the adsorption–desorption equilibrium should be reached at very high temperatures, with the following trend in the adsorption strength MH > MOH >> M. Relativistic periodic DFT calculations of the adsorption properties of group 1 and 2 elements, including elements 119 and 120, and of their hydrides and hydroxides, on the hydroxylated quartz surfaces.

Theoretical predictions of properties and adsorption behavior of group 1 and 2 elements, including elements 119 and 120, on the surface of gold from periodic DFT calculations

Properties of group 1 and 2 elements and their (oxy)hydrides, including those of elements 119 and 120, adsorbed on the gold (111) surface were calculated using the AMS ADF and periodic BAND software. The results show that all the group 1 elements’ species should adsorb well on the surface of gold, with the following sequence in the adsorption strength MH > M > MOH. The species of elements 119 and 120 should adsorb most weakly in group 1 and 2, respectively, due to the strong relativistic stabilisation of the 8s AO. A reversal of trends in the adsorption energies, E ads, and other properties is established in group 1 and 2 from the elements of the 6th row, Cs and Ba, respectively, due to reversal in the energies and space distribution of the ns AO. The latter is caused by the relativistic stabilisation and contraction of the ns AOs. The obtained E ads values of the group 1 and 2 elements and their compounds, above 180 kJ/mol, mean that very high temperatures of the gas phase chromatography column with gold plated detectors are required to observe an adsorption equilibrium, i.e. a peak of the distribution of decay events in the column.

Theoretical predictions of properties and volatility of chlorides and oxychlorides of group-4 elements. I. Electronic structures and properties of MCl₄ and MOCl₂ (M = Ti, Zr, Hf, and Rf).

Relativistic, infinite order exact two-component, density functional theory electronic structure calculations were performed for MCl4 and MOCl2 of group-4 elements Ti, Zr, Hf, and element 104, Rf, with the aim to predict their behaviour in gas-phase chromatography experiments. RfCl4 and RfOCl2 were shown to be less stable than their lighter homologs in the group, tetrachlorides and oxychlorides of Zr and Hf, respectively. The oxychlorides turned out to be stable as a bent structure, though the stabilization energy with respect to the flat one (C(2v)) is very small. The trend in the formation of the tetrachlorides from the oxychlorides in group 4 is shown to be Zr < Hf < Rf, while the one in the formation of the oxychlorides from the chlorides is opposite. All the calculated properties are used to estimate adsorption energy of these species on various surfaces in order to interpret results of gas-phase chromatography experiments, as is shown in Paper II.

Theoretical predictions of properties and volatility of chlorides and oxychlorides of group-4 elements. II. Adsorption of tetrachlorides and oxydichlorides of Zr, Hf, and Rf on neutral and modified surfaces.

With the aim to interpret results of gas-phase chromatography experiments on volatility of group-4 tetrachlorides and oxychlorides including those of Rf, adsorption enthalpies of these species on neutral, and modified quartz surfaces were estimated on the basis of relativistic, two-component Density Functional Theory calculations of MCl4, MOCl2, MCl6(-), and MOCl4(2) with the use of adsorption models. Several mechanisms of adsorption were considered. In the case of physisorption of MCl4, the trend in the adsorption energy in the group should be Zr > Hf > Rf, so that the volatility should change in the opposite direction. The latter trend complies with the one in the sublimation enthalpies, ΔH(sub), of the Zr and Hf tetrachlorides, i.e., Zr < Hf. On the basis of a correlation between these quantities, ΔH(sub)(RfCl4) was predicted as 104.2 kJ/mol. The energy of physisorption of MOCl2 on quartz should increase in the group, Zr < Hf < Rf, as defined by increasing dipole moments of these molecules along the series. In the case of adsorption of MCl4 on quartz by chemical forces, formation of the MOCl2 or MOCl4(2-) complexes on the surface can take place, so that the sequence in the adsorption energy should be Zr > Hf > Rf, as defined by the complex formation energies. In the case of adsorption of MCl4 on a chlorinated quartz surface, formation of the MCl6(2-) surface complexes can occur, so that the trend in the adsorption strength should be Zr ≤ Hf < Rf. All the predicted sequences, showing a smooth change of the adsorption energy in the group, are in disagreement with the reversed trend Zr ≈ Rf < Hf, observed in the "one-atom-at-a-time" gas-phase chromatography experiments. Thus, currently no theoretical explanation can be found for the experimental observations.

Theoretical predictions of properties and gas-phase chromatography behaviour of carbonyl complexes of group-6 elements Cr, Mo, W, and element 106, Sg

Fully relativistic, four-component density functional theory electronic structure calculations were performed for M(CO)6 of group-6 elements Cr, Mo, W, and element 106, Sg, with an aim to predict their adsorption behaviour in the gas-phase chromatography experiments. It was shown that seaborgium hexacarbonyl has a longer M-CO bond, smaller ionization potential, and larger polarizability than the other group-6 molecules. This is explained by the increasing relativistic expansion and destabilization of the (n - 1)d AOs with increasing Z in the group. Using results of the calculations, adsorption enthalpies of the group-6 hexacarbonyls on a quartz surface were predicted via a model of physisorption. According to the results, -ΔHads should decrease from Mo to W, while it should be almost equal--within the experimental error bars--for W and Sg. Thus, we expect that in the future gas-phase chromatography experiments it will be almost impossible--what concerns ΔHads--to distinguish between the W and Sg hexacarbonyls by their deposition on quartz.

Theoretical predictions of properties and gas-phase chromatography behaviour of bromides of group-5 elements Nb, Ta, and element 105, Db

Fully relativistic, four-component density functional theory electronic structure calculations were performed for MBr(5), MOBr(3), MBr(6)(-), KMBr(6), and MBr(5)Cl(-) of group-5 elements Nb, Ta, and element 105, Db, with the aim to predict adsorption behaviour of the bromides in gas-phase chromatography experiments. It was shown that in the atmosphere of HBr/BBr(3), the pentabromides are rather stable, and their stability should increase in the row Nb < Db < Ta. Several mechanisms of adsorption were considered. In the case of adsorption by van der Waals forces, the sequence in volatility of the pentabromides should be Nb < Ta < Db, being in agreement with the sublimation enthalpies of the Nb and Ta pentabromides. In the case of adsorption by chemical forces (on a quartz surface modified with KBr∕KCl), formation of the MBr(5)L(-) (L = Cl, Br) complex should occur, so that the volatility should change in an opposite way, i.e., Nb > Ta > Db. This sequence is in agreement with the one observed in the "one-atom-at-a-time" chromatography experiments. Some other scenarios, such as surface oxide formation were also considered but found to be irrelevant.

Structure, spectroscopic properties, and photochemistry of the hydroxymethoxy radical

The hydroxymethoxy (HMO) radical is proposed to be the primary product of photodissociation of the atmospherically important hydroxymethyl hydroperoxide (HMHP). This transient species is still unknown and the present study provides theoretical predictions of properties, spectroscopy, and photochemistry of this radical for the first time. Structures, harmonic frequencies, vertical and vibrationally resolved absorption spectra are computed for several electronic states, using state-of-the-art ab initio electronic structure methods. The lowest excited state, absorbing in the mid to near infrared, seems to be the most promising candidate for spectroscopic identification of HMO. The electron affinity of 2.232 eV and the characteristic photodetachment spectrum is also predicted to be suitable for experimental investigations. By contrast, the B state absorbing around 3.5 eV is proposed to undergo fast photodissociation, forming CH(2)O and OH, and thus appears less useful for spectroscopic detection of HMO. However, the photodissociation may be important for the atmospheric chemistry of HMHP. Ionization of HMO will also lead to dissociation or rearrangement of the cation and will yield only unspecific spectra.

Theoretical Predictions of Properties and Chemical Behavior of Superheavy Elements

Fully relativistic electronic structure calculations have been performed for gas phase and aqueous phase compounds of elements 104 through 108. Based on these calculations, volatility and complex formation, as well as trends in these properties, have been predicted. The transactinide compounds were shown to exhibit properties very similar to those of the lighter homologs in the respective chemical groups. Some deviations from the observed trends were established.