Vibrational dynamics of acetate in D2O studied by infrared pump–probe spectroscopy

Abstract

Solute-solvent interactions between acetate and D(2)O were investigated by vibrational spectroscopic methods. The vibrational dynamics of the COO asymmetric stretching mode in D(2)O was observed by time-resolved infrared (IR) pump-probe spectroscopy. The pump-probe signal contained both decay and oscillatory components. The time dependence of the decay component could be explained by a double exponential function with time constants of 200 fs and 2.6 ps, which are the same for both the COO asymmetric and symmetric stretching modes. The Fourier spectrum of the oscillatory component contained a band around 80 cm(-1), which suggests that the COO asymmetric stretching mode couples to a low-frequency vibrational mode with a wavenumber of 80 cm(-1). Based on quantum chemistry calculations, we propose that a bridged complex comprising an acetate ion and one D(2)O molecule, in which the two oxygen atoms in the acetate anion form hydrogen bonds with the two deuterium atoms in D(2)O, is the most stable structure. The 80 cm(-1) low-frequency mode was assigned to the asymmetric stretching vibration of the hydrogen bond in the bridged complex.

Binary Mixtures of Choline Acetate and Tetrabutylammonium Acetate with Natural Organic Acids by Vibrational Spectroscopy and Molecular Dynamics Simulations

“…From the analysis of the spectra, we can affirm that the pure ion pair ChAc is strongly coupled, as observed in other cholinium-based ionic liquids: − the asymmetric stretching of COO groups , (ν CO ), indeed, is at a low wavenumber (1579 cm –1 ) and the stretching of OH (ν OH ) is around 3200 cm –1 .The strong coupling between choline and acetate was confirmed also by the DFT calculations. ChAc was modeled at the B3LYP/6-31G** level of theory performing the calculations on a cluster composed by three ion pairs.…”

Efficient Vibrational Energy Transfer through Covalent Bond in Indigo Carmine Revealed by Nonlinear IR Spectroscopy

“…In solution phase, a vibrationally excited polyatomic system usually undergoes a “two-step relaxation process”, − including a rapid intramolecular energy transfer that is usually referred to as intramolecular vibrational energy redistribution (IVR) and a slow intermolecular vibrational energy transfer process (VET). Vibrational relaxations involving multiple modes have been modeled and reported previously. − In the case of indigo carmine/DMSO system, both CO and CC vibrators undergo the intra- and intermolecular dissipation processes.…”

Anharmonicities and coherent vibrational dynamics of phosphate ions in bulk H2O

“…The opposite cross-peak tilt at T =200 fs is the fingerprint of the non-rephasing contribution whose amplitude is non-oscillating and the relative contribution to the absorptive 2D signal is maximal at this T . We note that oscillatory features in time-resolved vibrational spectroscopy can arise from broad-band excitations of either a quantum beat of coupled modes within the pulse spectrum 49,51-56 or a wave packet of low-frequency modes in an impulsive Raman process 57,58 . The presented analysis of 2D spectra in terms of rephasing and non-rephasing contributions allows to safely assign the origin on the basis of the contributing Liouville space pathways and reveals coherent beating at unique frequency positions of cross peaks that only arise due to quantum beats of the coupled ν S (PO − 2 ) and ν AS (PO − 2 ) modes.…”

“…We note that oscillatory features in time-resolved vibrational spectroscopy can arise from broad-band excitations of either a quantum beat of coupled modes within the pulse spectrum 49,[51][52][53][54][55][56] or a wave packet of low-frequency modes in an impulsive Raman process. 57,58 The presented analysis of 2D spectra in terms of rephasing and non-rephasing contributions allows the safe assignment of the origin on the basis of contributing Liouville space pathways and reveals coherent beating at unique frequency positions of cross peaks that only arise due to quantum beats of the coupled n S (PO 2…”