Phosphonic acids, such as amino tris­(methylenephosphonic acid) (ATMP) and diethylenetriamine penta­(methylenephosphonic acid) (DTPMP), are used in various applications, including scale control, water treatment, and corrosion protection. The increasing use of these compounds has raised environmental concerns due to their slow degradation, which can lead to eutrophication and the release of toxic byproducts. The detection of these compounds using surface-enhanced Raman spectroscopy (SERS) can be an interesting tool for monitoring their presence in aquatic environments. However, the vibrational characterization of these compounds has not yet been fully described in the literature. In this study, phosphonic acids ATMP and DTPMP were analyzed using density functional theory (DFT) and Raman/SERS spectroscopy. The theoretical spectra obtained were consistent with the experimental spectra, and the vibrational assignments aligned with those of organic compounds with similar structures reported in the literature. Furthermore, SERS analysis revealed bands for both compounds at concentrations up to 50 ppm (1.67 × 10^–4 mol L^–1 for ATMP and 8.72 × 10^–5 mol L^–1 for DTPMP).

This study investigates an unusual behavior observed in the Raman spectra of natural rhodochrosites under ambient conditions and varying temperature and pressure. While the typical MnCO₃ spectrum is maintained, the relative intensities of libration (L) and translation (T) bands exhibit significant variations, potentially linked to changes in the Mn²⁺ state within the crystal lattice. Mapping experiments under ambient conditions revealed intensity inversions in lattice modes depending on the sampling region and excitation wavelength. Initially attributed to laser-induced degradation, this phenomenon was ruled out by temperature-dependent Raman spectroscopy, which showed no significant intensity changes even under conditions promoting sample degradation. Further investigations under hydrostatic pressure revealed a decrease in L band intensity, potentially indicating crystal compaction and modified cation–anion interactions. Thermodynamic parameters were calculated using both linear and quadratic fitting methods, demonstrating that while linear fitting provides acceptable results for temperature-dependent analysis, a quadratic approach is crucial for pressure-induced changes, influencing the value of calculated Gruneisen and anharmonicity parameters. This work highlights the sensitivity of Raman spectroscopy to subtle changes within the rhodochrosite structure and provides valuable insights into the intricate interplay of temperature, pressure, and Mn ion configuration in this mineral.