the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Oct 2023
Quantum Yields of CHDO above 300 nm
Luc Vereecken
Abstract. The photolysis of mono-deuterated formaldehyde, CHDO, is a critical process in the deuterium-enrichment of stratospheric hydrogen formed from methane. A consistent description of the quantum yields of the molecular and radical channels of the CHDO photolysis is deduced from literature data. The fluorescence measurements of Miller and Lee (1978) provided a first data set to deduce the product quantum yields. An alternative analysis is provided by the measured quantum yield spectrum for the radical channel of the CD2O photolysis by McQuigg and Calvert (1969), which is corrected for wavelength dependency and combined with the CH2O quantum yield spectrum to provide an approximation for CHDO. Both approaches provide consistent results. Finally, the findings of Troe (1984, 2007) enable the specification of the pressure dependence of the quantum yield for CH2O and CD2O and, hence, for CHDO. We find that the radical channel does not show a pressure dependence, whereas the molecular channel is dominated by tunneling and quenching processes. For modeling purposes, simplified representations are given, and as an example for their application, the altitude dependence of the ratio of J(CHDO → HD+CO) and J(CH2O → H2+CO) is provided.
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Ernst-Peter Röth and Luc Vereecken
Status: open (extended)
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RC1: 'Comment on egusphere-2023-2254', Anonymous Referee #1, 07 Nov 2023
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This paper brings life to old data from which consistent formulations of the molecular and radical channel quantum yields in CHDO photolysis are extracted. The results probably merit publication after considering a number of comments.
In general, the Figure captions appear to be of the “insider type” and not such that the Figures can be viewed and understood by the reader without a meticulous inspection of the text. The criticism applies to most of the figures; taking Figure 1 as example: "Comparison of the measured data by Miller and Lee (1978) (full dots) with the pressure dependent part of the fitted function fkt(M]) for different wavelengths in nm as indicated." Without consulting the text, the reader is left wondering: Which data? Which function? What is Q(M)?
Table 1 is not "self-consistent" in the sense that all symbols are defined either in the Table caption or in footnotes (De1 and De2).
The first Figure referenced in the text is Figure 4a in Section 3 (line 106). It is as if the authors have done a last-minute paragraph swap. Caption to Figure 4a: "Wavelength dependence of the contributions of the 3 terms of equation F7 to the total quantum yield of the CHDO photolysis at 10 hPa (a) and 1030 hPa (b)." At this point in the text, the reader is about to be introduced to where the rate coefficients k1, k2, k5 and k6 origin (that is, Table X in the paper by Miller and Lee, 1978). The rate coefficients and the derived rate coefficients (k3, k4, k6 and k7) are then summarized in Table 2. The authors add confusion by citing Table 2 of Miller and Lee (it is actually TABLE II) and then their own Table 2 a few lines later.
Equation (F4) is a pseudo-equation that does not add to the value of the paper and it would perhaps be better write equation (F3) in the form below and maybe indicate the wavelength dependency as well:
Table 2. The excitation wavelengths listed are rounded numbers from the Miller and Lee (ML) 1978 publication that states: the out-of-plane bending mode (n4) is the inducing mode for radiative transitions and also the promoting mode for the nonradiative transitions. Why not use the wavelengths given by ML ? Why are the 316.2 nm ML data not used? The ML 320.2 nm data are entered in Table 2 with 329 nm excitation – why? Have the authors located misprints in the ML TABLE II? If yes, this should be communicated. The 329, 344 and 353 nm data for k5 and k6 in Table 2 do not correspond to any t-numbers in the ML TABLE II. Where do these numbers come from? The 329 nm data (ML 320.2 nm) refers to fluorescence from the 1141 (S1) state (n1 corresponds to the CH str), and the “next lower vibrational level” would be the 41 (S1) state, for which to fluorescence data are found for 353 nm excitation. However, this is the only case not involving the n2 mode (C=O str). Obviously, there are no data for the “next lower vibrational levels” of the 43 and 41states involving n2, yet numbers appear for k5 and k6 in Table 2. In summary, the selection of data could be better described.
Line 154. The authors state: The pivot wavelength 1/ε0 is 348.6 nm, as published in Nilsson et al. 155 (2014). Maybe they should mention that the 348.8 nm origins from quantum chemistry calculations of the barriers to dissociation H-CHO, H-CDO, D-CHO and D-CDO.
Line 168. “optimal values” should probably be “optimized values”
Table 3, Line 185. The A-value for k1 must have been derived taking the k1-value for 329 nm as an outlier. Are there other examples of data-massage? There are no error estimates included in Table 3 to indicate the validity of the smoothing procedure.
Line 242. The numbers in the equation are not the same as those given in the reference, but are apparently rounded. However, some of the numbers are rounded outside the error limits given in the reference.
Figure captions, Line 562. As mentioned, the Figures including captions should preferably be self-consistent. In general, this is not the case.
Citation: https://doi.org/10.5194/egusphere-2023-2254-RC1
Ernst-Peter Röth and Luc Vereecken
Ernst-Peter Röth and Luc Vereecken
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