FTIR spectroscopic investigations of supersaturated NaClO4 aerosols

Abstract

Supersaturated NaClO4 aerosols have been studied using a Fourier transform infrared (FTIR) spectrometer coupled with an aerosol flow tube (AFT). Compared with previous Raman results, the water O-H stretching envelope in the supersaturated solutions of NaClO4 aerosols was more structured in response to changing RH, revealing at the same time the existence of water monomers weakly hydrogen-bonded with ClO4- at extremely high concentrations. Due to enhanced ion interactions in the supersaturated solutions of NaClO4 aerosols, the formation of contact ion pairs (CIPs) could be observed without component decomposition for the nondegenerate nu1 band of ClO4-, and the degenerate nu3 band of ClO4- was successfully related to the formation of CIPs in NaClO4 solutions. Based on these observations, a new mechanism featured by the attack of ClO4- upon hydrated Na+ for CIPs formation in the supersaturated solutions of NaClO4 aerosols was further proposed. The anhydrous NaClO4, characterized by the upper limit deliquescence relative humidity (DRH) of approximately 43% and the disappearance of the nu1 band of ClO4- in the infrared spectra, was observed to form on the silicon windows at low RHs.

Crystallization dynamics of supersaturated NaClO4 aerosols studied by high-speed photography

“…Previous studies suggested that supersaturated NaClO 4 aerosols effloresced at ~10% RH to form metastable anhydrous particles [5,6] . Therefore, their morphologic changes at ~10% attracted special attention in this work.…”

“…Under the supersaturated state, crystallization of aerosol droplets is mainly affected by kinetic factors, resulting in metastable solids instead of thermodynamically stable ones [2][3][4] . It was found that supersaturated NaClO 4 aerosol droplets were crystallized to form metastable anhydrous particles at ~10% relative humidity (RH) rather than NaClO 4 ·H 2 O with an equilibrium RH of ~40% [5,6] . The crystallization of supersaturated aerosols and the formation of metastable solids are the two fundamental problems of crystallography and atmospheric sciences [5][6][7][8][9][10][11][12] .…”

“…It was found that supersaturated NaClO 4 aerosol droplets were crystallized to form metastable anhydrous particles at ~10% relative humidity (RH) rather than NaClO 4 ·H 2 O with an equilibrium RH of ~40% [5,6] . The crystallization of supersaturated aerosols and the formation of metastable solids are the two fundamental problems of crystallography and atmospheric sciences [5][6][7][8][9][10][11][12] . Though the properties of metastable solids have attracted much interest of researchers, there are a few reports on the investigations of the dynamics of metastable solidification.…”

Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H2O ligands and ClO4– anions in [Ba(H2O)3](ClO4)2

“…For an isolated ClO 4 – anion all these four modes are RS active and ν 3 and ν 4 are IR active only. However, when the high symmetry structure of the ClO 4 – anions is even slightly perturbed, then its degenerated vibrational modes may split and some of the inactive modes may become active …”

Phase transition in [Ca(NH3)6](ClO4)2 studied by neutron scattering methods and far infrared spectroscopy

“…The assignments of these vibrations were proposed by comparing their frequencies with the literature data for several similar ionic amminemetal(II) complexes [7][8][9]. All characteristic bands frequencies of the internal vibrations of NH 3 perturbed somehow, its degenerated vibrational modes may split and some of the inactive modes may be activated [10,11]. The proton-weighted phonon density of states function G( ) was calculated according to the formula (1) for double differential crosssection of neutrons scattered on protons in the sample [12]:…”