Infrared spectroscopy of matrix isolated polycyclic aromatic hydrocarbons. 2. PAHs containing five or more rings

Matrix isolation techniques have been used to measure the mid-infrared spectra of the polycyclic aromatic hydrocarbons (PAHs) benzo[e]pyrene, pentacene, perylene, benzo[ghi]perylene, coronene, and 1,12:2,3:4,5: 6,7:8,9:10,11-hexabenzocoronene. The observed band positions and relative strengths are compared to previous lab studies and with theoretical calculations, where available.(1) Agreement with other available laboratory data is excellent. Comparisons with theory indicate that density functional theory (DFT) does an excellent of describing the majority of the infrared active fundamentals of the PAHs considered here. Band positions typically agree to better than 5 cm(-1), with the worst disparities usually being less than 15 cm(-1). Matches in band strengths are not as precise, but are generally good to better than 30-50% for most strong and moderate bands and are good to factors of 2-4 for weaker bands. The theory predicts CH stretching band strengths that are too strong by a factor of about 2.