The growth mechanism of sulfuric acid clusters: Implication for the formation of cloud condensation nuclei

- The linear structure is more stable as compared to the bent and the orbicular conformations.
- The length of the linear mode polymers increases linearly along with the degree of polymerization.
- The diameter of the central ring in orbicular conformation increases distinctly from 3.441 Å in tetramer to 7.543 Å in nonamer.
- The IR spectra exhibit distinct variations along with both the DP and the coupling modes.
- The sulfuric acid can aggregate with a larger DP in linear mode.

The investigation on the growth mechanism of sulfuric acid clusters is helpful for the understanding about the formation of cloud condensation nuclei. The sulfuric acid may aggregate in linear, bent, or orbicular modes with two types of hydrogen bonds, viz. OH…OH and OH…O=S. The length of the linear mode polymers increases linearly along with the degree of polymerization (DP). The bent conformation distorts into the linear configuration when the DP is over 6. The diameter of the central ring generated by OH…OH hydrogen bonds in orbicular conformation increases distinctly from 3.441 Å in tetramer to 7.543 Å in nonamer. The IR spectra exhibit distinct variations along with both the DP and the coupling modes. As can be employed to infer the detailed geometrical structures of sulfuric acid polymers. The linear structure is more stable as compared to the bent and the orbicular conformations. The variation of the Gibbs free energy indicates that the sulfuric acid can aggregate with a larger DP in linear mode. The temperature effect on the stability of the sulfuric acid polymer is more significant as compared with that of the pressure. The complex with high DP tends to be more stable at higher temperature, while the complex with low DP prefers low temperature. The findings are helpful for further study on atmospheric aerosol growth and the formation of cloud nucleation.