Rate Constants for Reactions of HCCO and HCCCO Radicals with O₂ over the Temperature Range 243–423 K

Abstract

A pulsed laser photolysis–photoionization mass spectrometer system has been employed to measure the rate constants of HCCO + O2 and HCCCO + O2 over the temperature range 243–423 K in 1.2–8.4 Torr of He or N2. Radicals of HCCO and HCCCO were produced by 193 nm ArF laser photolysis of ethyl ethynyl ether and methyl propiolate, respectively. HCCO was photoionized by a Kr resonance lamp with a CaF2 window (10.03 eV), and HCCCO was ionized by a Xe lamp with a sapphire window (8.44 eV). Both ions were detected as parent ions in a quadrupole mass spectrometer. From analysis of the time profiles of the ion signals for various O2 concentrations, the overall rate constants at 298 K are represented by the values k 2 = (6.3 ± 1.0) × 10–13 for HCCO + O2 and k 5 = (5.7 ± 0.6) × 10–12 for HCCCO + O2 in the units cm3 molecule–1 s–1. The rate coefficients for the two reactions can be described by k 2(T) = (1.5–0.7 +1.5) × 10–12 exp[−(225 ± 220)/T] and k 5(T) = (1.8–0.9 +1.9) × 10–12 exp[(343 ± 228)/T] in the units cm3 molecule–1 s–1 over the temperature range 243–423 K.

Spectroscopic Identification of the Heterocumulenic Isocyanatoborane Radical HBNCO

“…A central issue in the internal dynamics is whether these canonical forms correspond to isolable forms or to resonance structures of a single observable geometry. Heterocumulenes HCCCO and NCCO are two typical free radicals with 27 electrons. − According to the rules for Lewis structure stability, there are two favorable canonical structures . As shown in Scheme , configuration ( I ) is characterized by a bent C–CO unit, and the unpaired electron is localized at the sp 2 -hybridized carbonyl C c atoms in both radicals.…”