Estimation of the reaction rate for the formation of CH3O from H + H2CO: Implications for chemistry in the solar system

$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

“…Also shown is a model employing the Prinn & Barshay (1977) model with the revised reaction rates of Griffith & Yelle (1999) which shows an even poorer match to the spectral morphology, since in this model even less CH 4 has formed. However, the depth of the CH 4 absorption at ∼3.3 μm falls between that seen in the spectra predicted by the Yung et al (1988) and Prinn & Barshay (1977) Prinn & Barshay (1977) model in blue, the Prinn & Barshay (1977) model with the revised reaction rates of Griffith & Yelle (1999) in magenta, and a model following the Yung et al (1988) chemistry in red. All models have been smoothed to 60 Å FWHM to match observations.…”

“…However, as seen in Fig. 26, the Prinn & Barshay (1977) model does not match the shape of the L-band spectrum, whereas the chemical equilibrium model and the Yung et al (1988) model provide reasonable matches to the shape and absolute flux levels -the CH 4 absorption predicted by both models is identical within the internal uncertainties of the model atmospheres. Also shown is a model employing the Prinn & Barshay (1977) model with the revised reaction rates of Griffith & Yelle (1999) which shows an even poorer match to the spectral morphology, since in this model even less CH 4 has formed.…”

“…All models have been smoothed to 60 Å FWHM to match observations. correct reaction timescale might have a value slightly below that of Yung et al (1988), or alternatively, the vertical mixing could be more efficient than assumed in the BT-Settl models. Freytag et al (2010) suggest such additional mixing can be produced by convectively driven gravity waves, though the mixing efficiency of such waves in terms of an equivalent diffusion coefficient is still under investigation.…”

“…between 1000 and 1500 K, the diffusion coefficient in this part of the overshoot region would best characterise our model, corresponding to 10 7 −10 8 cm 2 /s in the ε Indi Ba model. In addition, we consider several reaction pathways and timescales besides the one from Prinn & Barshay (1977), on which the Saumon et al (2003) models are based, notably the revised time scale for the scheme of Prinn & Barshay (1977) suggested by Griffith & Yelle (1999), and the reaction scheme of Yung et al (1988) (see also Griffith & Yelle 1999). Among these, the Yung et al (1988) model generally predicts the fastest conversion rates from CO to CH 4 , and the Prinn & Barshay (1977) model with the modified rates of Griffith & Yelle (1999) the slowest rates, implying the strongest CE departure effects.…”

“…Figure 25 shows the observed 2.27−2.35 μm spectrum, where the CO 2−0 overtone band (starting at 2.2935 μm) can be identified even on top of the octad band of CH 4 . For comparison, a chemical equilibrium model and non-CE model spectra, based on the reaction models of Prinn & Barshay (1977) and Yung et al (1988) respectively, are shown. The Prinn & Barshay (1977) model better reproduces the rotational series of the CO 2−0 R branch extending redwards from 2.2935 μm, but the CE and Yung et al (1988) models match the overall morphology better, including the 2.315 μm CH 4 bandhead.…”