title: Infrared spectroscopic probing of dimethylamine clusters in an Ar matrix.
abstract: Amines have many atmospheric sources and their clusters play an important role in aerosol nucleation processes. Clusters of a typical amine, dimethylamine (DMA), of different sizes were measured with matrix isolation IR (infrared) and NIR (near infrared) spectroscopy. The NIR vibrations are more separated and therefore it is easier to distinguish different sizes of clusters in this region. The DMA clusters, up to DMA tetramer, have been optimized using density functional methods, and the geometries, binding energies and thermodynamic properties of DMA clusters were obtained. The computed frequencies and intensities of NH-stretching vibrations in the DMA clusters were used to interpret the experimental spectra. We have identified the fundamental transitions of the bonded NH-stretching vibration and the first overtone transitions of the bonded and free NH-stretching vibration in the DMA clusters. Based on the changes in vibrational intensities during the annealing processes, the growth of clusters was clearly observed. The results of annealing processes indicate that DMA molecules tend to form larger clusters with lower energies under matrix temperatures, which is also supported by the calculated reaction energies of cluster formation.
authors.affiliation: Environment Research Institute, Shandong University, Shanda South Road 27, Shandong 250100, China. Electronic address: siyangli.cn@hotmail.com.
authors.forename: Siyang
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Henrik G
authors.initials: HG
authors.lastname: Kjaergaard
authors.affiliation: Environment Research Institute, Shandong University, Shanda South Road 27, Shandong 250100, China; Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark. Electronic address: lindu@sdu.edu.cn.
authors.forename: Lin
authors.initials: L
authors.lastname: Du
mesh_terms: D000336:Aerosols / Q000737:chemistry; D000393:Air Pollutants / Q000737:chemistry; D004123:Dimethylamines / Q000737:chemistry*; D008956:Models, Chemical; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013696:Temperature; D013816:Thermodynamics; D014732:Vibration
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D004123:Dimethylamines; C034516:dimethylamine
keywords: Aerosol nucleation; Dimethylamine clusters; Infrared (IR) spectroscopy; Matrix isolation