p-Nitroanisole/pyridine and p-nitroacetophenone/pyridine actinometers revisited: quantum yield in comparison to ferrioxalate
chemical actinometry, photochemistry, p-nitroacetophenone, pyridine, PNAP-PYR
Chemical actinometry is often used to measure irradiance in environmental photochemistry. Two widely adopted actinometers are p-nitroanisole/pyridine (PNA-pyr) and the related but less popular p-nitroacetophenone/pyridine (PNAP-pyr). We report that PNA-pyr predicts systematically lower (−29%) photon irradiance than the well-characterized ferrioxalate actinometer. Thus, quantum yields previously determined using PNA-pyr should be correspondingly lower. Experiments at various pyridine concentrations produced an updated equation for the pyridine (pyr) dependence of the PNA-pyr quantum yield: Φ = 0.29[pyr] + 0.00029. Additionally, we present a standard molar absorption spectrum of PNA for future use. A comparison between PNA-pyr and PNAP-pyr suggests the previously reported PNAP-pyr quantum yield is also too high. Preliminary results suggest a suitable equation for the PNAP-pyr system: Φ = 7.4 × 10–3[pyr] + 1.1 × 10–5.
Environmental Science & Technology
Laszakovits, J.R.*, S.M. Berg*, B.G. Anderson*, J.E. O’Brien*, K.H. Wammer, C.M. Sharpless. 2016. “p-Nitroanisole/pyridine and p-nitroacetophenone/pyridine actinometers revisited: quantum yield in comparison to ferrioxalate.” Environmental Science and Technology Letters, 4:11-14. DOI: 10.1021/acs/estlett.6b00422