Vibrational relaxation of azide ions in liquid-to-supercritical water

Abstract

The dynamics of vibrational energy relaxation (VER) of the aqueous azide anion was studied over a wide temperature (300 K ≤ T ≤ 663 K) and density (0.6 g cm(-3) ≤ ρ ≤ 1.0 g cm(-3)) range thereby covering the liquid and the supercritical phase of the water solvent. Femtosecond mid-infrared spectroscopy on the ν(3) band associated with the asymmetric stretching vibration of the azide anion was used to monitor the relaxation dynamics in a time-resolved fashion. The variation of the vibrational relaxation rate constant with temperature and density was found to be rather small. Surprisingly, the simple isolated binary collision model is able to fully reproduce the experimentally observed temperature and density dependence of the relaxation rate provided a local density correction around the vibrationally excited solute based on classical molecular dynamics simulations is used. The simulations further suggest that head-on collisions of the solvent with the terminal nitrogen atoms rather than side-on collisions with the central nitrogen atom of the azide govern the vibrational energy relaxation of this system. Finally, the importance of hydrogen bonding for the VER dynamics in this system is briefly discussed.

A novel intermolecular potential to describe the interaction between the azide anion and carbon nanotubes

“…Albeit the relatively large number of works on nitrogen chains, not so many other species were considered in a confined environment. In particular, despite the extensive literature investigating the spectroscopic features of the azide ion in crystal or gas phase [34][35][36][37][38][39][40][41][42] as well as solvated [43][44][45][46][47][48][49][50][51][52][53][54][55], N − 3 was never studied in a confined environment. Considering that N − 3 often represents a precursor in the synthesis of energetic molecules, e.g.…”

Water in Hydration Shell of an Azide Ion: Structure and Dynamics of Solute-water Hydrogen Bonds and Vibrational Spectral Diffusion from First Principles Simulations At Supercritical Condition

“…Aqueous azide ion solution in this case serves as a model system to study the dynamics and spectral diffusion of solute and solvent molecules because of its absorption in the mid IRregion and dependence of its vibrational frequency on solvent fluctuations. [44][45][46][47][48][49][50] Also, its sophisticated vibrational energy relaxation ranging from room temperature to the supercritical region makes the molecular ion an excellent probe for the solvent dynamics at supercritical condition.…”

“…According to their work, the solvent molecule in the vicinity of the ion plays an important role in the spectral diffusion of azide ion at varying condition, however they did not observe any dependence of the vibrational relaxation on the thermal fluctuation and thus found the spectral diffusion of azide asymmetric stretch mode almost unchanged over that wide temperature limits. Followed by the work of Tominaga et al [49], in 2011, Vohringer et al [50] simulated the vibrational relaxation of azide asymmetric stretch mode over a wider range of temperatures (300 K≤T≤663 K) and densities (0.6 g cm −3 ≤T≤1.0 g cm −3 ) using Femtosecond mid-infrared spectroscopy and classical molecular dynamics simulations. First time they were able to give a clear picture of the vibrational spectral diffusion of the azide asymmetric stretch mode as a function of the temperature and density and showed the effect of the local density corrections on the vibrational spectral diffusion of asymmetric stretch mode of the azide ion.…”

Ab initio molecular dynamics studies of hydrogen bonded structure, molecular motion, and frequency fluctuations of water in the vicinity of azide ions

“…The decay of the frequency-frequency time correlation function of the asymmetric stretch mode of azide ion can be experimentally studied through time dependent infrared spectroscopy and directly related with the fluctuations of the solvation shell. Various experimental [37][38][39][40][41][42][43][44][45] studies have been performed to investigate the dynamical behavior of water molecules in the solvation shells of azide ions such as the frequency fluctuations and dynamics of hydrogen bonds (HBs) in the vicinity of the ions. Generally, it has been reported that the vibrational spectral diffusion of azide asymmetric stretching mode takes place through the hydrogen bond decay channel which points to strong coupling between the azide molecular a) E-mail: amalen@iitk.ac.in ion and surrounding water molecules.…”

“…These authors also calculated the absorption line shape and integrated three pulse-echo intensity for the asymmetric stretch mode of azide ion. A subsequent study 45 based on a combination of femtosecond time resolved pump-probe experiment and classical molecular dynamics simulation has shown that solvent molecules generally interact with the terminal nitrogens of the triatomic linear ion and relax the initial asymmetric stretching excitation through such intermolecular interactions.…”