The dynamics of nanoparticles in a carrier gas are governed by the physical and chemical nature of the surface. The total surface area can be divided into an “active” and a “passive” part. The active surface is the surface on which transfer of momentum, energy, and mass from the gas to the particle takes place. The experiments show that the active surface may be determined in physically very different in situ experiments such as measuring the mobility b, the diffusion constant D, or the mass transfer coefficient K of the particle. The concept of the active surface manifests itself in scaling laws Kb=const, KD=const, and Yb=const, found valid over a large range of particle shapes and sizes. Y is the yield of low energy photoelectrons from the particles upon irradiating the carrier gas with light of energy below the ionization energy of the carrier gas molecules but above the photoelectric threshold of the particles. While K, D and b are independent of the chemical nature of the particles as far as we know today, the simultaneous measurement of Y provides a chemical fingerprint of the particles and allows one to observe, in combination with pulsed lasers as sources of light, the dynamical changes of the active surface while the nanoparticle is interacting with the carrier gas.
A laminar diffusion flame of methane was investigated using time-of-flight mass spectroscopy with two-photon UV laser ionization. Benzenoid polycyclic aromatic hydrocarbons (PAHs) up to 788 amu (C64H20) were detected in the combustion gases. Only the most compact PAHs are formed in the flame. The observed groups of PAH peaks with 24 amu spacings belong to PAHs with constant hydrogen content and are separated by 26 amu gaps. The sequences of PAH peaks with 24 amu spacing are explained by a repetitive bay closure mechanism. The first PAH of a constant H-sequence is proposed to form by a dimerization process. The PAHs observed can be arranged in a repetitive pattern in Dias’s formula periodic system.
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