Spectrometry CIDNP

In the above section the photodevices that can be employed to reach the appropriate reactant state were outlined. In the remainder of the chapter, the devices and instruments for monitoring the subsequent change and determining the rate characteristics will be discussed. By far the most frequently employed diagnostic techniques are optical absorption and emission spectrometry other less-used methodologies include light-scattering spectrometry, and the electron-spin-based spectroscopies, such as EPR, ENDOR, and CIDNP. These last three are not addressed in this review. 

The El-induced fragmentation of gaseous [4 + 2]- and [2 + 2]dicyclopentadiene radical cations has been studied by Roth and coworkers using Fourier transform ion cyclotron resonance mass spectrometry, and compared to the cleavage of these ions in solution using chemically induced dynamic nuclear polarization (CIDNP). Both in the gas and in the liquid phase, the isomers of the molecular ions formed by single C—C bond cleavage were observed. It is noteworthy that these distonic ions were termed non-vertical radical cations. 

The overall diagram of evolution of the excited states and reactive intermediates of a photoinitiating system working through its triplet state can be depicted in Scheme 10.2 [249]. Various time resolved laser techniques (absorption spectroscopy in the nanosecond and picosecond timescales), photothermal methods (thermal lens spectrometry and laser-induced photocalorimetry), photoconductivity, laser-induced step scan FTIR vibrational spectroscopy, CIDEP-ESR and CIDNP-NMR) as well as quantum mechanical calculations (performed at high level of theory) provide unique kinetic and thermodynamical data on the processes that govern the overall efficiency of PIS. 

---