In:
The Journal of Chemical Physics, AIP Publishing, Vol. 129, No. 10 ( 2008-09-14)
Kurzfassung:
The NaNO3 droplets with sizes of 1–5μm generated from a nebulizer were deposited on a ZnSe substrate in a Fourier transform infrared attenuated total reflection (FTIR-ATR) chamber. After solidification of the droplets with dry N2 gas passing through the chamber, the solid NaNO3 particles were monitored by in situ FTIR-ATR spectra in cycles of deliquescence and efflorescence processes with varying relative humidities (RHs). With an increase in the RH, a dominant peak at ∼3539cm−1, together with three relatively weak peaks at ∼3400, ∼3272, and ∼3167cm−1, in the O–H stretching band of water was resolved by the high signal-to-noise ratio FTIR-ATR spectra. The dominant peak and the three relatively weak peaks were contributed by the water monomers and the aggregated water molecules adsorbed on the surfaces of solid NaNO3 particles, respectively. When the RH approached ∼72%, slightly lower than the deliquescence RH (74.5%), the band component at ∼3400cm−1 became the main peak, indicating that the water monomers and the aggregated water molecules aggregated to form a thin water layer on the surfaces of solid NaNO3 particles. A splitting of the ν3-NO3− band at 1363 and 1390cm−1 at the RH of ∼72%, instead of the single ν3-NO3− band at 1357cm−1 for the initial solid NaNO3, was observed. We suggested that this reflected a phase transition from the initial solid to a metastable solid phase of NaNO3. The metastable solid phase deliquesced completely in the region from ∼87% to ∼96% RH according to the fact that the ν3-NO3− band showed two overlapping peaks at 1348 and 1405cm−1 similar to those of bulk NaNO3 solutions. In the efflorescence process of the NaNO3 droplets, the ν1-NO3− band presented a continuous blueshift from 1049cm−1 at ∼77% RH to 1055cm−1 at ∼36% RH, indicating the formation of contact ion pairs between Na+ and NO3−. Moreover, in the RH range from ∼53% down to ∼26%, two peaks at 836 and 829cm−1 were observed in the ν2-NO3− band region, demonstrating the coexistence of NaNO3 solid particles and droplets.
Materialart:
Online-Ressource
ISSN:
0021-9606
,
1089-7690
Sprache:
Englisch
Verlag:
AIP Publishing
Publikationsdatum:
2008
ZDB Id:
3113-6
ZDB Id:
1473050-9
