The hyperfine excitation of OH radicals by He

Abstract

Abstract. Hyperfine-resolved collisions between OH radicals and He atoms are investigated using quantum scattering calculations and the most recent ab initio potential energy surface, which explicitly takes into account the OH vibrational motion. Such collisions play an important role in astrophysics, in particular in the modelling of OH masers. The hyperfine-resolved collision cross sections are calculated for collision energies up to 2500 cm −1 from the nuclear spin free scattering S-matrices using a recoupling technique. The collisional hyperfine propensities observed are discussed. As expected, the results from our work suggest that there is a propensity for collisions with ΔF = Δj. The new OH−He hyperfine cross sections are expected to significantly help in the modelling of OH masers from current and future astronomical observations.

Hyperfine excitation of CH and OH radicals by He

“…Each Λ-doublet level has two hyperfine components that correspond to two different hyperfine quantum numbers F max and F min , with F max > F min . In the case of OH-He, it was shown (Marinakis et al 2016) that the cross-sections were larger in the following order:…”

“…Therefore, only changes in the relative orientation of the j and I vectors can lead to a change in the magnitude of the resultant F vector (Corey & Alexander 1988). Because of the tendency for preservation of the j vector and of the general propensity for ∆F = ∆ j, a propensity for ∆F = 0 is often observed (Corey & Alexander 1988;Offer et al 1994;Marinakis et al 2016). As discussed in previous work (Dagdigian et al 1989;Marinakis et al 2015), there is a propensity for transitions into antisymmetric rotational levels (Π(A ) levels, meaning F 1 f , F 2 e), in He-CH(X) upward transitions.…”

“…As discussed in the case of OH-He (Marinakis et al 2016), the energy difference in these hyperfine levels is negligible and can be disregarded in the discussion on propensities at usual temperatures. Each Λ-doublet level has two hyperfine components that correspond to two different hyperfine quantum numbers F max and F min , with F max > F min .…”

“…A brief review of the calculations of astrophysical interest can be found in Roueff & Lique (2013). Recently, we derive new collisional rotational rate coefficients for the excitation of OH and CH by He (Kalugina et al 2014;Marinakis et al 2015Marinakis et al , 2016Marinakis et al , 2019. Together with the very recent OH-H 2 and CH-H 2 collisional data (Kłos et al 2017;Dagdigian 2018), these rate coefficients should enable an accurate determination of CH and OH abundance in molecular clouds.…”

Atomic cluster collisions: ISACC-2015 (7th International Symposium)*

“…So, multiconfiguration time-dependent Hartree calculations are presented by Valdés and Prosmiti for the Ar 2 ICl vdW cluster characterizing the corresponding states to different isomers [43]. Capture approximations beyond a statistical quantum mechanical method, for atom-diatom reactions, are analyzed by Barrios et al [44]; for modelling of OH masers, hyperfine resolved collisions of this radical with helium atoms are presented by Marinakis et al [45]; the reaction of hydroperoxil radicals with ozone, in the presence of water molecules and also inside a water cage of twenty molecules, which is crucial in the atmosphere, is addressed by Viegas and Varandas [46]. Related to chiral molecular recognition phenomena, density functional theory (DFT) is applied by Pelayo et al to study the enantiospecific adsorption of cysteine on a chiral Au 34 cluster [47].…”