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Mineral dust aerosol plays an important role in the Earth's radiative budget on both regional and global scales. To better understand the impact of this component of the Earth's atmosphere, the extinction spectra for several key components of mineral dust aerosol have been measured in an environmental aerosol reaction chamber. The extinction spectra are measured over a broad wavelength range, which includes both IR (650 to 5000 cm−1) and UV‐Vis (12,500 to 40,000 cm−1) spectral regions. Experimental data are compared with Mie theory simulations derived from available literature optical constants. In a few cases, we have needed to modify the published optical constant data sets to ensure Kramers‐Kronig consistency. In general, the Mie‐based simulations are in excellent agreement with experimental data over the full IR‐UV spectral range, except in the immediate neighborhood of the IR resonance absorption lines where particle shape effects on the resonance line profiles can be significant.

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We have studied the structure and dissociation dynamics of the weakly bound bimolecular complex Al+(C2H4) by photodissociation spectroscopy in the 216–320 nm spectral region. Experimental studies are supported by ab initio electronic structure calculations of the ground and low-lying excited states of the complex. Al+ is the dominant photofragment observed throughout the absorption profile. C2H4+ charge transfer product is also observed for shorter photolysis wavelengths, λ<252 nm. The Al+–C2H4 bond dissociation energy is measured as D0=0.37±0.15 eV. Three molecular absorption bands are observed and assigned to the transitions (2 1A1,1 1B1,1 1B2←1 1A1) in C2v equilibrium complex geometry. The excited states are of predominantly charge-transfer character correlating with the product channel Al(3s23p)+(C2H4)+. The 2 1A1 and 1 1B2←1 1A1 absorption bands appear broad and structureless. This observation is consistent with ab initio results that suggest a pathway for rapid nonadiabatic dissociation through a 1 1B2–1 1A1 surface crossing facilitated by a stretch in the C–C bond of ethylene. In contrast the 1 1B1←1 1A1 molecular band shows significant vibrational structure. Spectroscopic analysis yields a band origin (000=40 042 cm−1) and corresponding vibrational mode frequencies for the 1 1B1 excited state. The observed modes have been assigned to the intermolecular Al–C2H4 stretch of a1 symmetry (ν2=230 cm−1), the Al–C2H4 out-of-plane wag with b1-symmetry (ν3=328 cm−1), and two intramolecular ethylene modes of a1 symmetry at 1264 and 1521 cm−1. The assignment for these higher frequency ethylene modes is not conclusive.