甲醛光解过程中CO和H2的极端同位素分馏:理论与实验。

IF 2.8 2区 化学 Q3 CHEMISTRY, PHYSICAL
The Journal of Physical Chemistry A Pub Date : 2025-03-06 Epub Date: 2025-02-19 DOI:10.1021/acs.jpca.4c07516
Luisa Pennacchio, Zacharias Liasi, Andreas Erbs Hillers-Bendtsen, Thomas Röckmann, Kurt V Mikkelsen, Matthew S Johnson
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引用次数: 0

摘要

甲醛(HCHO)是大气中有机分子分解的重要中间体。它是大气中含量最丰富的羰基,也是降解后CO和H2的主要来源。同位素分析为分子过程提供了有价值的见解,加深了我们对大气转变的理解。我们提出了一个基于rice - ramspberger - kassel - marcus (RRKM)分析的同位素依赖的甲醛光解同位素分馏模型,用新的和已有的实验数据验证了该模型,并用它来描述光解动力学同位素效应(KIEs)及其压力依赖性。利用RRKM理论分别用CCSD(T)/奥格-cc- pvtz、ωB97X-D/奥格-cc- pvtz和CASPT2/奥格-cc- pvtz计算了S0、S1和T1态的分解率。我们考虑了同位素物HCHO、DCHO、DCDO、D13CHO、H13CHO、HCH17O、HCH18O、H13CH17O和H13CH18O。我们发现同位素取代显著影响态密度,影响单分子分解速率和碰撞能量转移。在氙灯下,实验光解速率从50 mbar下jHCHO/jHCH18O = 1.027±0.006到1000 mbar下jHCHO/ jddo = 1.418±0.108。该模型准确地再现了KIEs中的实验压力趋势,揭示了H2中高度依赖的氘富集不能仅用压力效应来解释,还必须考虑波长依赖性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Extreme Isotopic Fractionation in CO and H2 Formed in Formaldehyde Photolysis: Theory and Experiment.

Formaldehyde (HCHO) is an important intermediate in the breakdown of organic molecules in the atmosphere. It is the most abundant atmospheric carbonyl, and a major source of CO and H2 upon degradation. Isotopic analysis offers valuable insights into molecular processes, deepening our understanding of atmospheric transformations. We present a model of the isotope-dependent photolytic isotopic fractionation of formaldehyde incorporating Rice-Ramsperger-Kassel-Marcus (RRKM) analysis, validate the model with new and pre-existing experimental data, and use it to describe photolytic kinetic isotope effects (KIEs) and their pressure dependencies. RRKM theory was used to calculate decomposition rates of the S0, S1, and T1 states, using CCSD(T)/aug-cc-pVTZ, ωB97X-D/aug-cc-pVTZ, and CASPT2/aug-cc-pVTZ, respectively. We considered isotopologues HCHO, DCHO, DCDO, D13CHO, H13CHO, HCH17O, HCH18O, H13CH17O, and H13CH18O. We find that isotopic substitution notably affects the density of states, influencing rates of unimolecular decomposition and collisional energy transfer. Experimental photolysis rates ranged from jHCHO/jHCH18O = 1.027 ± 0.006 at 50 mbar to jHCHO/jDCDO = 1.418 ± 0.108 at 1000 mbar using a xenon lamp. The model accurately reproduced experimental pressure trends in KIEs, revealing that altitude-dependent deuterium enrichment in H2 cannot be explained by pressure effects alone and must also consider wavelength dependence.

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来源期刊
The Journal of Physical Chemistry A
The Journal of Physical Chemistry A 化学-物理:原子、分子和化学物理
CiteScore
5.20
自引率
10.30%
发文量
922
审稿时长
1.3 months
期刊介绍: The Journal of Physical Chemistry A is devoted to reporting new and original experimental and theoretical basic research of interest to physical chemists, biophysical chemists, and chemical physicists.
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