I. Determination of chemical reaction rate constants by numerical nonlinear analysis: differential methods

TL;DR

This paper introduces nonlinear gradient-based methods to determine chemical reaction rate constants from experimental data without requiring initial concentration knowledge, revealing new semi sinusoidal concentration effects.

Contribution

It develops and validates nonlinear analysis techniques as alternatives to standard methods, suitable for experiments with unknown initial conditions.

Findings

Gradient methods are consistent with standard approaches.

Reactions showed semi sinusoidal concentration changes.

Potential new effects not predicted by current models.

Abstract

The primary emphasis of this work on kinetics is to illustrate the a posteriori approach to applications, where focus on data leads to novel outcomes, rather than the a priori tendencies of applied analysis which imposes constructs on the nature of the observable. The secondary intention is the development of appropriate methods consonant with experimental definitions. By focusing on gradients, it is possible to determine both the average and instantaneous rate constants that can monitor changes in the rate constant with concentration changes as suggested by this theory. Here, methods are developed and discussed utilizing nonlinear analysis which does not require exact knowledge of initial concentrations. These methods are compared with those derived from standard methodology. These gradient methods are shown to be consistent with the ones from standard methods and could readily serve as alternatives for studies where there are limits or unknowns in the initial conditions, such as in the burgeoning fields of astrophysics and astrochemistry, forensics, archeology and biology . All four reactions studied exhibited semi sinusoidal-like change with reactant concentration change which standard methods cannot detect, which seems to constitute the observation of a new effect that is not predicted by current formulations, where the possibility that the observations are due to artifacts from instrumental errors or the optimization method is reasoned as unlikely since the experiments were conducted by different groups at very different times with different classes of reactions.