Gas-Phase Vibrational Spectroscopy and Ab Initio Study of Organophosphorous Compounds: Discrimination between Species and Conformers

Abstract

Gas phase vibrational spectra of dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), and triethyl phosphate (TEP) have been measured using FTIR spectroscopy. For DMMP, TMP, and TEP, most of the infrared active vibrational modes have been observed in the 50-5000 cm (-1) spectral range, allowing an unambiguous discrimination between the three molecules. The vibrational analysis of the spectra was performed by comparing with MP2 and B3LYP harmonic and anharmonic force field ab initio calculations. The extension to anharmonic calculations provides the best agreement for the mid-infrared and the near-infrared spectra, but they do not improve the harmonic frequency predictions in the far-infrared domain. This part of the vibrational spectra associated with collective and nonlocalized vibrational modes presents the largest frequency differences between the two lowest energy conformers of DMMP and TMP. These two conformers were taken into account in the vibrational assignment of the spectra. Their experimental evidence was obtained by deconvoluting vibrational bands in the mid-infrared and in the far-infrared regions, respectively. For TEP, the conformational landscape appears very complicated at ambient temperature, and a further analysis at low temperature is required to explain the vibrational features of each conformer.

Probing Coherent Vibrations of Organic Phosphonate Radical Cations with Femtosecond Time-Resolved Mass Spectrometry

“…To identify potential coherently excited vibrations, the normal modes for both the neutral and cation geometries of DMMP, DEMP, and DIMP were computed and compared to experimental IR and Raman measurements [34,35,36,37] (Supplementary Materials, Tables S7–S9 and Figures S1–S3). The rough agreement of the computed spectra of the DMMP, DEMP, and DIMP neutrals with experimental measurements is similar to recent computational studies of the IR spectra of these molecules [33,38]. Based on these computed normal modes, the ionization-induced geometrical changes, and experimentally observed oscillation frequencies, we focused on a cluster of three normal modes labeled A , B , and C with computed frequencies for the neutrals and cations given in Table 2 and illustrations of the motions given in Figure 7.…”

“…To predict whether similar geometrical changes occur in DEMP and DIMP, the neutral and cation geometries were computed at the B3LYP/6-311+G* level. The computed geometries of DMMP agree with previous results [18,31,33] and serve to benchmark the method for DEMP and DIMP. Figure 6 depicts the neutral and cation geometries of DMMP, DEMP, and DIMP with the P=O, P–O, P–C, and C−O bond lengths and O–P–O angle labeled.…”

Structural analysis of xCsCl(1−x)Ga2S3 glasses by means of DFT calculations and Raman spectroscopy

“…The presence of several imaginary wavenumbers in the calculations demonstrates that, even for the monomers, the HF method was not suited to efficiently localise the minima of the potential energy surfaces. For dimers and tri‐clusters, the semi‐empirical DFT calculations were used in preference to the MP2 method because of its lower calculation cost and because the DFT method often gives more conclusive results for the harmonic vibrational frequency determination 14. All the DFT calculations were performed with the Becke15 three parameters hybrid exchange functional and the Lee‐Yang‐Parr correlation functional (B3LYP) 16.…”

Jet-cooled rovibrational spectroscopy of methoxyphenols using two complementary FTIR and QCL based spectrometers

“…Nevertheless, the unambiguous conformer assignments obtained in the case of a rather large polyatomic molecule such as 3MP with four conformations significantly populated is a proof of the efficiency of high resolution QCL jet-cooled spectroscopy to analyze the conformational landscape of flexible molecules and to disentangle rovibrational signatures in a dense spectral region. The non-localized low-energy vibrational modes lying in the far-IR region also present a great potential for an efficient conformational discrimination [31] but, compared to the near-IR and UV domains, the available setups in this domain still lack of sensitivity. In a near future, new generation of QCL far-IR sources [32,33] will offer real opportunities to probe and resolve at low temperature the lowest energy vibrational bands of individual conformers even for highly flexible molecules characterized by a rich conformational landscape.…”