| Abstract [eng] |
In this work, the bromomalonaldehyde (C3H3BrO2) molecule was investigated using vibrational spectroscopy combined with the matrix isolation technique. Due to the molecule’s low volatility, the Knudsen cell method was employed to enable its introduction into the experimental system. The main objectives of the study were to determine possible molecular conformations, to record infrared absorption spectra of the isolated molecule, and to investigate its molecular dynamics by evaluating potential conformational changes in different matrix environments and at various temperatures. Theoretical calculations were performed using B3LYP, M06, and MP2 methods with the cc-pVDZ basis set, implemented in the Gaussian 16 software package on the “VU HPC” Saulėtekis supercomputer at the Faculty of Physics, Vilnius University. The calculations identified eight low-energy molecular conformations, with the CCC conformer determined to be the most stable. Experimental infrared absorption spectra were recorded in argon, nitrogen, and neon matrices. Spectral analysis indicates the presence of two conformers, denoted CCC and TTC, in all studied matrices. Temperature-dependent experiments showed that the relative population of these conformers remains constant across the investigated temperature range, indicating that the energy barrier for conformational interconversion is too high for transitions to occur under the experimental conditions. Additionally, a proton tunneling effect was observed in the argon matrix, while no such effect was detected in nitrogen and neon matrices. This behavior is attributed to the properties of the matrix environments, namely, stronger intermolecular interactions in nitrogen and restricted molecular motion due to the small lattice size in neon matrices. A comparative analysis of theoretical methods showed that their accuracy depends on the spectral region considered. The MP2 method provides consistently good agreement with experimental data across all regions; however, it does not show a clear advantage over the other methods in any specific case. The M06 method yields the best agreement with experimental spectra in the 900–1500 cm⁻¹ region, while the B3LYP method more accurately reproduces the carbonyl (C=O) stretching region, reflecting differences in their ability to describe electronic structure associated with specific vibrational modes. The obtained results demonstrate that the matrix environment significantly influences the behavior of the investigated molecule and confirm that matrix isolation spectroscopy combined with quantum chemical calculations is an effective approach for structural characterization, analysis of intramolecular dynamics, and observation of proton tunneling in low-volatility systems. |
