Collisional rates for rotational transitions in H₂CO and their application

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• 作者：Monika Sharma^a ; ^{monika3273@yahoo.in" class="auth_mail} ; M.K. Sharma^a ; ^{mohitkumarsharma32@yahoo.in" class="auth_mail} ; U.P. Verma^a ; ^{upv.udai@gmail.com" class="auth_mail} ; Suresh Chandra^b ; ^{suresh492000@yahoo.co.in" class="auth_mail}
• 关键词：ISM ; molecules ; H2CO molecule ; Collisional rates
• 刊名：Advances in Space Research
• 出版年：15 July 2014
• 年：2014
• 卷：54
• 期：2
• 页码：252-260
• 全文大小：378 K

文摘

Formaldehyde (H₂CO) has always been of great importance for physicists. To analyze its spectrum collisional rate coefficients are required. Their computation is quite tedious job. We have calculated collisional rate coefficients for rotational transitions between 23 levels of each of the ortho and para species of H₂CO for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed with the help of the computer code MOLSCAT where the colliding partner is taken as the He atom. The required potential for interaction between H₂CO and He is calculated with the help of the software gaussian 2003 where the coupled-cluster CCSD(T) method and cc-pVTZ basis set are used. The Basis Set Superposition Errors (BSSE) are accounted for. The wave functions for the asymmetric top molecule H₂CO are expressed in terms of the Wigner D  -functions and the expansion coefficients $g_{J蟿}^K$ are obtained. For the interaction potential obtained with the help of gaussian 2003, MOLSCAT is used to derive the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ as a function of energy E   of the colliding partner. After averaging the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ over the Maxwellian distribution, the parameters Q(L,M,M^′|T)$Q(L\text{,}M\text{,}{M}^{\prime }|T)$ as a function of the kinetic temperature T in the cloud are obtained. The results are compared with the available data.

We have also calculated radiative transition probabilities (Einstein A  -coefficients) for transitions between 23 rotational levels for each of the ortho and para species of H₂CO. Finally, for ortho-H₂CO, we have solved a set of 23 statistical equilibrium equations coupled with 39 equations of radiative transfer and discussed anomalous absorption of the 1₁₁-1₁₀$1_{11}-1_{10}$ transition of H₂CO at 4.830 GHz.