Low-temperature collisional quenching of NO A2Σ+(v′ = 0) by NO(X2Π) and O2 between 34 and 109 K

Abstract

We present measurements of collisional fluorescence quenching cross sections of NO(A(2)Σ(+), v' = 0) by NO(X(2)Π) and O2 between 34 and 109 K using a pulsed converging-diverging nozzle gas expansion, extending the temperature range of previous measurements. The thermally averaged fluorescence quenching cross sections for both species show a monotonic increase as temperature decreases in this temperature range, consistent with earlier observations. These new measurements, however, allow discrimination between predictions obtained by extrapolating fits of previous data using different functional forms that show discrepancies exceeding 120% for NO and 160% for O2 at 34 K. The measured self-quenching cross section is 52.9 Å(2) near 112 K and increases to 64.1 Å(2) at 35 K, whereas the O2 fluorescence quenching cross section is 42.9 Å(2) at 109 K and increases to 58.3 Å(2) at 34 K. Global fits of the quenching cross section temperature dependence show that, when including our current measurements, the low temperature behavior of the quenching cross sections for NO and O2 is better described by a parameterization that accounts for the long-range interactions leading to the collisional deactivation via an inverse power law model.

Molecular properties and excited state van der Waals potentials in the NO A2Σ+ + O2 XΣg− collision complex

“…To put our results in perspective of experimental work 9,11–14 and assumptions concerning possible quenching pathways, we can support the hypothesis regarding the formation of a collision complex, which can explain the negative dependence of the quenching cross section observed in NO A 2 Σ + + O 2 X 3 Σ g − system. Although we only provide plot of the quartet PES, a CASPT2 scan allows us to support the formation of this collision complex both on the quartet and doublet surfaces.…”

“…Then, Settersten et al 13 observed a negative temperature dependence of the quenching cross-section, and proposed a well-depth of −41 cm −1 for the collision complex. Later, in 2014, Sánchez-González et al 14 study collisions between NO A 2 Σ + and O 2 X 3 Σ g − at lower temperatures than Settersten et al , 13 and proposed a potential well depth of −39 cm −1 for the collision complex. Also, they stressed on the importance of attractive intermolecular multipole interractions, which become increasingly efficient at reduced collision velocities.…”

Development of a pulsed uniform supersonic gas expansion system based on an aerodynamic chopper for gas phase reaction kinetic studies at ultra-low temperatures

“…Based on the technique developed by Smith and co-workers, Sánchez-Gónzalez et al (2012) built a pulsed uniform supersonic flow apparatus in order to be exploited as a laser diagnostic development tool. In a recent publication, they presented results of collisional quenching of NO(A 2 Σ + , v ′ = 0) by NO(X 2 Π) and O 2 at temperatures as low as 34 K (Sánchez-Gónzalez et al, 2014). Following a different direction, Oldham et al (2014) developed a new method for pulsing a gas.…”

Low Temperature Kinetics of the Reaction Between Methanol and the CN Radical

“…Rowe and co-workers 26 developed the use of CRESU flows to study gasphase kinetics and this technique has since been used to characterize many ion-neutral reactions, [27][28][29][30][31] neutral-neutral reactions, 8,12,[32][33][34][35][36] and collisional energy transfer processes. [37][38][39][40] A detailed summary of the reactions studied using the CRESU technique was published recently. 41 Radical-neutral reactions are thought to be an important destruction route for gas-phase methanol at low temperatures.…”