Marine new particle formation (NPF) can affect cloud condensation nuclei (CCN) in the global atmosphere. Recently, iodic acid (IA) has been identified as a critical driver for marine NPF. However, atmospheric observations of IA cannot be associated with predicted particle formation rates. Given the complexity of atmospheric components, other species may promote IA particle formation. As an efficient stabilizer for acidic precursors, dimethylamine (DMA) has a wide distribution over the oceans. Hence, we investigated the nucleation process of DMA and IA under different atmospheric conditions and uncovered the corresponding nucleating mechanism using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that DMA can structurally stabilize IA via hydrogen and halogen bonds, and the clustering process is energy barrierless. Moreover, DMA can enhance the formation rate of IA clusters by five orders of magnitude, and its efficiency in promoting IA cluster formation is much higher than that of NH₃. Compared to the nucleation via sequential addition of IA, the IA-DMA nucleation plays a more dominant role in nucleation kinetic. Thus, the effect of DMA on enhancing IA cluster stability and formation rate cannot be ignored, especially in the regions near the source of IA and DMA emissions. Broadly, the proposed IA-DMA nucleation mechanism may help to explain some missing sources of particles and, thus intensive marine NPF events.

We have measured gas phase vibrational spectra of the bimolecular complex formed between methanol (MeOH) and dimethylamine (DMA) up to about 9800 cm⁻¹. In addition to the strong fundamental OH-stretching transition we have also detected the weak second overtone NH-stretching transition. The spectra of the complex are obtained by spectral subtraction of the monomer spectra from spectra recorded for the mixture. For comparison, we also measured the fundamental OH-stretching transition in the bimolecular complex between MeOH and trimethylamine (TMA). The enthalpies of hydrogen bond formation (ΔH) for the MeOH–DMA and MeOH–TMA complexes have been determined by measurements of the fundamental OH-stretching transition in the temperature range from 298 to 358 K. The enthalpy of formation is found to be −35.8 ± 3.9 and −38.2 ± 3.3 kJ mol⁻¹ for MeOH–DMA and MeOH–TMA, respectively, in the 298 to 358 K region. The equilibrium constant (K_p) for the formation of the MeOH–DMA complex has been determined from the measured and calculated transition intensities of the OH-stretching fundamental transition and the NH-stretching second overtone transition. The transition intensities were calculated using an anharmonic oscillator local mode model with dipole moment and potential energy curves calculated using explicitly correlated coupled cluster methods. The equilibrium constant for formation of the MeOH–DMA complex was determined to be 0.2 ± 0.1 atm⁻¹, corresponding to a ΔG value of about 4.0 kJ mol⁻¹.