Journal of Theoretical and Computational Chemistry

Increasing chain length and end group substitution of polyynes play a crucial role in molecular electronics and nanomaterials. The studies on linear carbon chains are lesser when compared to other carbon allotropes like graphene, fullerenes, nanotube, etc. This prompted us to study the linear carbon chains of different lengths and substitutions. The electronic and optical properties of X–C${}_{\mathit{\text{n}}}$–X ($n=4$–15 and $\mathrm{\text{X}}={\mathrm{\text{NO}}}_2$, NH₂, CN, OH) molecules have been studied by using CAM-B3LYP/6-31G* level of theory of DFT methods. Linear carbon chains with odd values of n show lower bond length alternation (BLA) values similar to that of cumulenes and may have metallic property, but the substitution of donor/acceptor molecules does not decrease the BLA significantly. Molecular orbital analysis of linear carbon chains shows that NH₂ or NO₂ substituted polyynes have helical molecular orbitals for smaller chain lengths which may make a good candidate for molecular wires in molecular devices. As the chain length increases, the helicity decreases and finally disappears. Also, it is seen that for smaller odd values of $n$ for donor, substituted polyynes have a singlet ground, whereas all the odd $n$ values of acceptor substitution have triplet ground state.

Sulfonylureas are an important group of herbicides widely used for a range of weeds and grasses control particularly in cereals. However, some of them tend to persist for years in environments. Hydrolysis is the primary pathway for their degradation. To understand the hydrolysis behavior of sulfonylurea herbicides, the hydrolysis mechanism of metsulfuron-methyl, a typical sulfonylurea, was investigated using density functional theory (DFT) at the B3LYP/6-31$+$G(d,p) level. The hydrolysis of metsulfuron-methyl resembles nucleophilic substitution by a water molecule attacking the carbonyl group from aryl side (pathway a) or from heterocycle side (pathway b). In the direct hydrolysis, the carbonyl group is directly attacked by one water molecule to form benzene sulfonamide or heterocyclic amine; the free energy barrier is about 52–58kcalmol${}^{-1}$. In the autocatalytic hydrolysis, with the second water molecule acting as a catalyst, the free energy barrier, which is about 43–45kcalmol${}^{-1}$, is remarkably reduced by about 11kcalmol${}^{-1}$. It is obvious that water molecules play a significant catalytic role during the hydrolysis of sulfonylureas.

This paper investigates the simulation of a modified Hamilton–Jacobi equation in order to provide a classical wavefront-based formulation of reaction dynamics. Here, the wavefront is interpreted as minimizing a particular action functional. The method is rooted in the geometric optics and an eikonal equation is typically used for describing the light wave propagation. We have introduced a general formulation for reaction force surface (RFS) and a host of several force-based properties, which offer a reinvigorated understanding of the occurrence of a reaction event at molecular level. The calculation is performed on a model potential energy surface representing the hydrogen transfer reaction in malonaldehyde.

Tunneling ionization of vibrationally excited CS₂ molecules in their ground electronic state is calculated using molecular orbital Ammosov–Delone–Krainov theory (MO-ADK) considering bond length-dependence and bond angle-dependence. The tunneling ionization rates and the corresponding electron density are calculated respectively for different initial states. A relationship between laser intensity and the molecular orientation angle is determined and compared with experimental results, showing excellent agreement. Our calculations show that the primary contribution of vibration effect to CS₂ in tunneling ionization is due to the symmetric expansion mode.