SISSI H3 v3 — Spectral Integrity and Structural Similarity Index Official Method Specification (Version 3.0)

Assessing similarity between vibrational spectra is a fundamental task in spectroscopy, yet traditional methods—such as Pearson correlation, Euclidean distance, and cross-correlation—capture only broad intensity relationships and often fail to detect subtle but chemically meaningful structural differences. To address this limitation, SISSI H3 v3 introduces a curvature-based, region-wise framework for spectral coherence analysis. The method combines third-order derivatives, Gaussian–Gabor harmonic filtering, and weighted regional similarity to produce a normalized global coherence index in [0,1]. This Zenodo release provides a minimal demonstration of the SISSI H3 v3 methodology using xylene isomers (e.g., o-xylene and p-xylene). These molecules constitute an instructive benchmark: their spectra share strong overall similarity yet differ in fine vibrational features arising from positional substitution. The included example illustrates how SISSI H3 v3 captures these structural distinctions more effectively than intensity-based metrics. A comprehensive validation, including functional-group comparisons, isotopic substitution tests, theoretical vs experimental spectra, and a full NIST-derived coherence matrix, has been performed separately. These extended results confirm the physical consistency and structural discrimination power of SISSI H3 v3 and are available upon request from the corresponding author. This release establishes the official, citable implementation of SISSI H3 v3 and provides a concise, reproducible demonstration of its core capabilities.