Vibrational spectra of conformers of V and V x gases

Abstract

Based on ab initio quantum calculations of the electronic structure for different conformers of V and V x gases, we propose an assignment of the fundamental vibrational states of the compounds.Key words: electronic structure, adiabatic potential, vibrational state, conformers of V gas, molecular modeling.Introduction. V and V x gases (dimethylaminoethyl mercaptoethyl phosphonate) are highly toxic organophosphorus compounds posing an environmental threat. Identification of the indicated compounds from optical spectra is directly connected with model calculations of their geometric structure and vibrational spectra. The predictive possibilities for vibrational spectroscopy rest on ab initio methods for estimating the parameters of the adiabatic potential, determining the physicochemical properties of molecular compounds, including the position and intensity of bands in the optical spectra of polyatomic molecules.Establishing the correlation between the chemical structure and the optical spectrum of a molecular system in a specific phase state makes it possible to identify the individual molecular fragments of complicated analyte compounds. It is sufficient to refer to monographs [1][2][3]. In [4], the problem was discussed in detail for a number of organophosphorus compounds. In [5], the described possibilities of vibrational spectroscopy are applied to constructing structural dynamic models for known organophosphorus compounds: sarin, soman, tabun, and cyclosarin.For V and V x gases, available experimental data on the vibrational spectra are extremely limited [6]. However, the individual fragments of the compounds, such as paraffin hydrocarbons, have been well studied by vibrational spectroscopy methods [1]. Data on the vibrational spectra of phosphorus-, sulfur-, and nitrogen-containing fragments from monograph [1] also can be used to assess the results of a numerical experiment, along with the experimental data presented in [5].The presence of a large number of hydrogen atoms in the considered compounds requires estimation of the effect of anharmonic resonances when the numerical calculations are carried out. This is feasible with modern software, such as in [7].Results of Model Calculations and Discussion. The vibrational spectra were calculated in the anharmonic approximation of the theory of molecular vibrations. We gave preference to the ab initio quantum method DFT/B3LYP with basis sets from 6-31G*(**) to 6-311G*(**) [7].To solve the anharmonic vibrational problem in second-order perturbation theory, we used the model Hamiltonian [8]

Hydrolysis of a VX-like Organophosphorus Compound through Dissociative Chemisorption on the MgO(001) Surface

“…This simplification of the VX molecule structure drastically reduces the computational effort because it would be necessary to use a supercell replicating six and five times on the x ( a = 12.69 Å) and y ( b = 10.58 Å) axes, respectively, to keep these adsorbed VX molecules sufficiently distant in order to have neglectible dipole interactions between the images in our calculations. Likewise, organophosphorus nerve agents have different stable conformations, , and their chemical or biological environments can change the conformational energy . In this way, the DMPT molecule has fewer conformers and avoids steric effects of P–S bond cleavage on the MgO surface, thus allowing us to investigate the degradation of the typical V-agent group without substantially affecting the chemistry of the problem.…”