Catalytic effect of (H2O) n (n = 1-3) clusters on the HO2 + SO2 → HOSO + 3O2 reaction under tropospheric conditions.

The HO2 + SO2 → HOSO + 3O2 reaction, both without a catalyst and with (H2O) n (n = 1-3) as a catalyst, has been investigated using CCSD(T)/CBS//M06-2X/aug-cc-pVTZ methods, and canonical variational transition state theory with small curvature tunneling (CVT/SCT). The calculated results show that H2O exerts the strongest catalytic role in the hydrogen atom transfer processes of HO2 + SO2 → HOSO + 3O2 as compared with (H2O)2 and (H2O)3. In the atmosphere at 0 km altitude within the temperature range of 280.0-320.0 K, the reaction with H2O is dominant, compared with the reaction without a catalyst, with an effective rate constant 2-3 orders of magnitude larger. In addition, at 0 km, it is worth mentioning that the relevance of the HO2 + SO2 → HOSO + 3O2 reaction with H2O depends heavily on its ability to compete with the primary loss mechanism of HO2 radicals (such as the HO2 + HO2 and HO2 + NO3 reactions) and SO2 (such as the SO2 + HO reaction). The calculated results show that the HO2 + SO2 → HOSO + 3O2 reaction with H2O cannot be neglected in the primary loss mechanism of the HO2 radical and SO2. The calculated results also show that for the formation of HOSO and 3O2, the contribution of H2O decreases from 99.98% to 27.27% with an increase in altitude from 0 km to 15 km, due to the lower relative concentration of water. With the altitude increase, the HO2 + SO2 → HOSO + 3O2 reaction with H2O cannot compete with the primary loss mechanism of HO2 radicals. The present results provide new insight into (H2O) n (n = 1-3) catalysts, showing that they not only affect energy barriers, but also have an influence on loss mechanisms. The present findings should have broad implications in computational chemistry and atmospheric chemistry.

[Determination of trace chromium in rock samples by graphite furnace-AAS after microsphere phase separation extraction].

A new method for the determination of trace chromium in geological samples by graphite furnace atomic absorption spectrometry (GFAAS) with microsphere phase separation extraction was developed. With the existence of cosolvent of ethanol and solvent of 1-amylalcohol, the diphenylcarbazide reacted with Cr to form a complex in a homogenous phase. Then the complex was separated out with microsphere from the homogenous phase after a little water was added in the system. The operating conditions for phase separation and the heating program of graphite furnace were experimented and optimized. The interference of co-existent ions was studied. The results indicated that the microsphere phase separation extraction can be used to separate and extract the analyte, and also the microsphere can be used as the matrix modifier in the heating program of graphite furnace. As the cosolvent, the dosage of ethanol was about 0.2-0.5 times of the volume of water with the existence of 0.2-1.5 mL 1-amylalcohol. Under the optimum conditions, the linear range of the method was 0-10 microg x L(-1) and the detection limit was 0.057 microg x L(-1) with the relative standard deviation (RSD) of 3.3% (n=11). The concentration factor was 10 with 15 mL of water and 1.5 mL of 1-amylalcohol. The method has been applied to determine the concentration of Cr in geological samples and the analytical results are in agreement with the certified values.