This work raises questions about reaction mechanisms and their ramifications in relation to the model adopted by Sentman et al. (2008). The model adopted by Sentman et al. (2008) for the description of a sprite streamer promoted the {N 2 ( a ′ 1 Σ u − ) + N 2 → N 2 (B 3 Π g ) + N 2 } chemical reaction as the key chemical reaction, in the afterglow stage in their model, for forming N 2 (B 3 Π g ) species, which are responsible for N 2 first positive band system emissions. However, it is shown in this comment that Sentman et al. (2008) used an implicitly assumed value of the {N 2 ( a ′ 1 Σ u − ) + N 2 } quenching reaction rate constant for N 2 (B 3 Π g ) formation that is not supported by the conclusions in existing experimental works. It is also shown that there are additional competing chemical reactions forming N 2 (B 3 Π g ) which should be taken into account, some of which were not used in the model adopted by Sentman et al. (2008).
A statistical model, the local plasma approximation, is considered for the calculation of the logarithmic mean excitation energy for stopping power of chemically bound particles by taking into consideration chemical bonding. This statistical model is applied to molecular hydrogen and leads to results that suggest a value for the logarithmic mean excitation energy of molecular hydrogen that is larger than the accepted experimental and theoretical values.
The optical phenomena related to electrical discharges and to the technology of light production and material processing have been known for many decades. They have been adequately studied and widely applied. Therefore, exposure to the aforesaid optical phenomena as a learning exercise continues to impress and interest students in physics laboratories with essential learning results. With this in mind, we assembled a simple experimental apparatus which allows students to carry out experiments for the study of optical phenomena associated with electrical discharges and emission of radiation in a physics lab. A simple gas discharge flow system was utilized for observation of various coloured emissions as a function of experimental parameters, like molecular gas, discharge power, pressure and flow rate. Emission spectra were obtained using a laboratory spectrometer and emission bands were identified. Comparative spectra were also obtained with other light sources such as plasma globes and Geissler tubes of known gas composition. Distributions over vibrational states of some excited molecular states were measured and utilized to derive vibrational temperatures of vibrationally-electronically excited molecules.
The relationships between individual rotational or vibrational transition probabilities and the eigenvalues of the 172nd order relaxation matrix describing the rotation–vibration–dissociation coupling of ortho-hydrogen are explored numerically. The simple proportionality between certain transition probabilities and certain eigenvalues, which was found previously in the vibration–dissociation coupling case, breaks down. However, it is shown that at 2000°K the second smallest eigenvalue of the relaxation matrix (d n−2 ), hitherto regarded as determining the "vibrational" relaxation time, is related more to the transition probability assigned to the largest rotational gap which lies in the first (ν = 0 ↔ ν = 1) vibrational gap, i.e. to the transition ν = 0, J = 5 ↔ ν = 0, J = 7, than to anything else; this clearly supports an earlier suggestion that the transient which immediately precedes dissociation in a shock wave has to be regarded as a rotation–vibration relaxation time rather than a vibrational relaxation time. It is suggested that the Lambert–Salter relationships can be rationalized on this assumption.An analysis is then made of the energy uptake associated with each eigenvalue at three temperatures. At 500°K, the greatest energy increment is associated with two eigenvalues (d n−13 and d n−24 ) and can be characterized as essentially a rotational relaxation: the calculations confirm that the observed rotational relaxation time should first decrease and then increase with increasing temperature, as was recently found to be the case experimentally. At 2000°K, large energy increments are associated with several eigenvalues between d n−2 and d n−14 , and at 5000°K, with most of the eigenvalues d n−2 to d n−23 ; thus, the higher the temperature, the more complex is the (T–VR) rotation–vibration relaxation. Further, relaxation times for the same temperature measured by ultrasonic and shock-wave techniques need not agree.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVibrational energy transfer in a diffusion-flow cyclopropane-d2 systemJ. F. Burkhalter, E. Kamaratos, and B. S. RabinovitchCite this: J. Phys. Chem. 1980, 84, 5, 476–477Publication Date (Print):March 1, 1980Publication History Published online1 May 2002Published inissue 1 March 1980https://pubs.acs.org/doi/10.1021/j100442a003https://doi.org/10.1021/j100442a003research-articleACS PublicationsRequest reuse permissionsArticle Views17Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
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