Quantum mechanical effects in n-alkane droplets

According to quantum chemical (QC) calculations of a series of n-alkanes (CnH2n+2 at n = 1-8) the gap ΔHL between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases with increasing methylene group (-CH2-) number in the n-alkane chain. While the LUMO level appears to be relatively unchanged, in good agreement with experimental results, the HOMO level is unstabilized and ΔHL decreases from approximately 11 eV (methane) to 6.5 eV (n-octane). Comparative ab initio calculations show not only the quantum confinement effects (QCE) in n-alkanes in the gas phase due to the reduction of the ΔHL value, but also enabled selection of cost-effective methodologies for modelling long-chain n-alkanes (n > 8). The used methodologies include ‘Local Spin Density Approximation’, combining special exchange functional with suitable correlation functional. Electronic structures and energetics of n-pentane (C5H12) in the evaporation/condensation processes are studied to understand the molecular mechanism for these processes. Two main step processes, liquid (L) 1 liquid-gas (L-G) interface 2 gas (G), are analysed. While phase transformations between L and L-G is estimated as activation processes, it is found that there is no energy barrier in the transitions between L-G and G.