Matrix Isolation Infrared Spectroscopic and Theoretical Study of the Interaction of Water with Dimethyl Methylphosphonate

Abstract

Matrix isolation infrared spectroscopy has been combined with theoretical calculations for the characterization of the 1:1 hydrogen-bonded complex between H 2 O and dimethyl methylphosphonate (DMMP). The symmetric O-H stretching mode was observed to shift 203 cm -1 to lower energy upon hydrogen bond formation, while a 32 cm -1 blue shift was noted for the H-O-H bending mode of the H 2 O subunit in the complex. These values compare extremely well with the (unscaled) shifts of -203 and +32 cm -1 , respectively, that were calculated theoretically at the MP2/6-31+G** level. Additional perturbed modes of the DMMP subunit were observed, shifted relative to the parent band position. The greatest perturbation was to the PdO stretching mode near 1270 cm -1

Infrared signature of micro-hydration in the organophosphate Sarin: an ab initio study

“…Increased hydration levels produced minimal variation in the IR frequency (for the lowest ΔG structures). The magnitude of the Sarin P=O bond stretch red shift was similar to the predicted Δν=-21 cm −1 shift [23], or the experimental Δν=19 cm −1 red shift in hydrated DMMP [36]. This red shift was also similar to that in methyl dichloro phosphate (Δν=-12 cm −1 ), and trimethyl phosphate (Δν=-17 cm −1 ) adsorbed to Si-OH surfaces [37].…”

“…Details of the H 2 O-phosphate hydrogen bond formation can be probed by calculating and comparing induced IR shifts for a wide range of hydrated clusters. Previous ab initio studies have predicted a reduction (red shift) in the P=O vibrational frequency of 30 cm −1 for the monohydrated DMP anion, a red shift of 32 cm −1 for the trihydrated DMP cluster [14,15], while the mono-hydrated DMMP cluster experienced a 21 cm −1 red shift [23]. The impact on other IR vibrations has also been discussed, including Lee and co-worker's simulation of the water complexation with DMMP, DIFP, Sarin, and Soman (GD).…”

“…Ab initio computational methods have previously proven to be useful in investigating OP micro-hydration and include studies of the dihydrogen phosphate (DHP) and dimethyl phosphate (DMP) anion [14][15][16], bisphosphonates [17][18][19], phosphate [20], polyphosphate anions [21], DMMP [22,23], the G-agent simulant diisopropyl fluorophosphate (DIFP), and Sarin [22]. Recently we reported ab initio studies of adsorption energetics for the micro-hydrated Sarin•nH 2 O (n=1-4) clusters, confirming that the primary interaction was hydrogen bonding between the Sarin P=O group and water [24].…”

“…In OPs the experimental variation in the IR vibration frequencies can be significant even at low levels of hydration, and highlights the need to better understand the impact of inter-molecular hydrogen bonding in these micro-hydrated species [23]. Details of the H 2 O-phosphate hydrogen bond formation can be probed by calculating and comparing induced IR shifts for a wide range of hydrated clusters.…”

Ambient Volatility of DMMP

“…The observed deviations from Raoult's law are largest at water partial pressures near 500 Pa. Recent theoretical calculations and infrared spectroscopy reported by Ault and co-workers [5] indicate that intermolecular hydrogen bonding between water and DMMP contributes significantly in explaining the phenomena reported herein.…”