Experimental and computational analysis of spectroscopic parameters of L-ascorbic acid (vitamin C) and its tautomers was investigated by Density Functional Theory (DFT) using B3LYP method. The optimized geometries and calculated vibrational frequencies were evaluated. The latter was compare with those of experimental values. The λ max values of L-ascorbic acid were found 259 (at pH = 3) experimentally, 238 and 247 nm calculated in the gas and water phase at TD-DFT methods, respectively.

A new potential function, which can in a simple and reasonable manner represent the molecular interaction of many kinds of hard-core fluids by varying the value of its parameter, is proposed. For prediction of thermodynamic properties of hard-core fluids such as the square-well (SW) and hard core Lennard-Jones (HCLJ), a simple perturbed equation of state (EOS) is derived by using the new potential function along with the Barker-Henderson perturbation theory. This method yields a simple and general analytical expression for each thermodynamic property of such fluids. The most important feature of these expressions is that they have no adjustable parameter and in some regions in which there is no simulation data for such hard-core fluids, such equation may be used to predict the needed data. The derived EOS in this work was successfully applied to predict thermodynamic properties of the SW and HCLJ fluids, for which the simulation data are available. The predicted results are in good agreement with both the computer simulation data and the well-known equations of state.