Room-Temperature Cavity Ring-Down Spectroscopy of Methylallyl Peroxy Radicals

Abstract

We report room-temperature cavity ring-down (CRD) spectra of the à ← X̃ electronic transition of 1-, 2-, and 3-methylallyl peroxy (MAOO•) radicals produced by 193 nm photolysis of methyl-substituted allyl chlorides in the presence of O2. Vibronic structure of experimentally observed spectra was simulated using calculated relative populations of MAOO• conformers, their electronic transition frequencies and oscillator strengths, as well as their vibrational frequencies and Franck–Condon factors of the à ← X̃ electronic transition. The reaction intermediate for the production of 1- and 3-MAOO• radicals, CH3CHCHCH2, is a resonance-stabilized free radical. CRD spectra of 1- and 3-MAOO• radicals obtained using different precursors suggest that allylic rearrangement between the two resonance structures (CH3CH=CHCH2 • and CH3CH•CH=CH2) is significantly faster than oxygen addition. Branching ratio between terminal and nonterminal oxygen addition was predicted to be 52:48 on the basis of calculated spin densities, which agrees qualitatively with the experimental CRD spectra of 1- and 3-MAOO• radicals.

Kinetics of 1- and 2-methylallyl + O2 reaction, investigated by photoionisation using synchrotron radiation

“…Stable neutral and cationic species were found for all three of them. The neutral species have recently been detected by cavity ringdown IR spectroscopy, 50 but detection by photoionisation is not possible, as discussed above. Their IEs were all computed to be around 8.30 eV with an almost planar CCCC framework in the cation.…”

A paired emitter–detector diode-based photometer for the determination of sodium hypochlorite adulteration in milk

“…To achieve this, photomultiplier tubes (PMTs), photodiode detector array (PDA), charge-coupled device (CCD), complementary metal-oxide semi-conductors (CMOS), and paired emitter detector diode (PEDD) have been developed 25 , 29 . Miniaturized spectrophotometers suffer from low detection sensitivity due to limited optical path length 30 , so approaches such as multireflection cells 31 , microfluidic systems, axial-direction 32 , liquid-core waveguides 33 , confined drop-based systems, and cavity ring-down spectroscopy 34 have been developed to improve sensitivity. Smartphones are mobile devices that combine computing and communication features, making them easier to use at the point of care.…”

Laser spectroscopy investigations of jet-cooled metal-containing free radicals.

“…The CRD apparatus employed the same dye laser source as the LIF but with significantly lower pulse energy (∼ 400 µJ). Details of the jet-cooled CRD apparatus 78,79 Beside random errors in the CRD experiments, one must consider the existence of possible systematic errors. We can identify two possible systematic errors that might make non-negligible contributions.…”

“…The CRD apparatus used in the present work is similar to the room-temperature CRD setup described in our previous papers 62,78 , except that the free radicals are produced by laser ablation under jet-cooled conditions as described in the main text. CRD mirrors…”