Direct measurements of removal rates of electronically excited NCO(Ã2Σ+(0,0,0)) by simple molecules

Direct measurements of absolute rate constants are reported for the collisional removal at room temperature of NCO(Ã2Σ+(0,0,0)) by O2(3Σg), N2(1Σ+g), NO(2Π), CO2(1Σ+g), N2O(1Σ+g), SO2(1A) and the photochemical precursor itself, phenyl isocyanate, PhNCO. NCO(X̃ 2Π32(0,0,0)) was prepared by infrared multiphoton dissociation (IRMPD) of PhNCO followed by tuneable dye laser pumping at the transition NCO(Ã2Σ+(0,0,0)) ← X̃ 2Π32(0,0,0)) coupled with laser-induced fluorescence (LIF) monitoring in the time-domain. Removal was found to be very efficient where the rate constants with the above gases were measured as 2.05±0.2, 15.2±0.2, 32.0±3.0, 8.52±0.4, 6.46±0.2, 27.1±1.0 and 51.8±5.0, respectively, in units of 10−11 cm3 molecule−1 s−1 (at a laser fluence of 43 J/cm2). An upper limit of the rate constant for the physical quenching of NCO(Ã) by Ar is also reported as < 2× 10−13 cm3 molecule−1 s−1. The resulting rate data are analysed and discussed in terms of the correlation with the potential well depth ((ϵ/k)12) of the collision partners, consequently yielding a pair well depth ((ϵ/k)12) of 94±15 K12 for NCO(Ã2Σ(0,0, 0)).