A new way of analyzing vibrational spectra. III. Characterization of normal vibrational modes in terms of internal vibrational modes

Abstract

The concept of characterizing normal vibrational modes l in terms of internal vibrational modes v typical of molecular fragments or structural subunits is n developed. Essential for this concept is the amplitude A A that provides the basis for a n quantitative comparison of modes l and v and, by this, facilitates the extraction of n chemical information out of vibrational spectra. Twelve possibilities of defining amplitude Ž . Ž . A A are tested with regard to a the physical basis of the definition of A A, b the dependence of A A on the set of internal parameters chosen to describe the molecule, and Ž . c the amount of chemical information transferred by A A. The two most promising candidates for a generally applicable amplitude A A are based on adiabatic internal modes and a comparison of l and v with the help of mass or force constant matrix. For the n practical testing of amplitude A A, three different criteria are developed.

A Critical Evaluation of Vibrational Stark Effect (VSE) Probes with the Local Vibrational Mode Theory

“…According to the CNM method [59], any normal vibrational mode l µ can be decomposed into local mode contributions from a non-redundant set of N vib local vibrational modes by calculating the overlap between each local mode vector a x n with this normal mode vector l µ as S nµ according to Equation (10)…”

“…In contrast, the CNM method as part of the Konkoli-Cremer local vibrational mode theory is directly based on vibrational spectroscopy and local modes can be smoothly transitioned to normal modes via adiabatic connection scheme [67]. In this sense, CNM analysis is superior than PED analysis as the former has better physical fundament in terms of vibrational spectroscopy [58][59][60]84].…”

“…However, to the best of our knowledge, no systematic study on the extent to which those commonly applied and/or potential vibrational Stark effect probes can meet this requirement, has been reported so far. To fill this gap, we used in this work as powerful tool the characterization of normal mode (CNM) procedure, which is an important part of the local vibrational mode analysis originally developed by Konkoli and Cremer [57][58][59][60]. CNM determines quantitatively to what extent the local stretching vibrational mode of the probe bond is decoupled from the other local vibrational modes of the probe, and therefore provides a unique measure to assess the qualification of a probe molecule.…”

Metal–Halogen Bonding Seen through the Eyes of Vibrational Spectroscopy

“…Also, the bond length is not a qualified bond strength descriptor. Numerous cases have been reported illustrating that a shorter bond is not always a stronger bond [65][66][67][68][69].…”

“…Detailed knowledge of these contributions from the prerequisites for achieving greater control over supramolecular architectures and for the fine-tuning and design of new materials is needed. Therefore, we introduce in this work a new quantitative measure for the intrinsic bond strength of metal-halogen bonding based on the local vibrational mode analysis first introduced by Konkoli and Cremer [67,68,73,74]. The investigation of 23 metal-halogen complexes derived from the dimers of Zordan and coworkers [25] focused in particular on answering the following questions:…”