Quantitative (υ, N, Ka) Product State Distributions near the Triplet Threshold for the Reaction H2CO → H + HCO Measured by Rydberg Tagging and Laser-Indu

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• 作者：W. Scott Hopkins ; Hans-Peter Loock ; Brí ; d Cronin ; Michael G. D. Nix ; Adam L. Devine ; Richard N. Dixon ; Michael N. R. Ashfold ; Hong-Ming Yin ; Steven J. Rowling ; Alexander Bü ; ll ; Scott H. Kable
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：October 2, 2008
• 年：2008
• 卷：112
• 期：39
• 页码：9283-9289
• 全文大小：197K
• 年卷期：v.112,no.39(October 2, 2008)
• ISSN：1520-5215

文摘

In this paper, we report quantitative product state distributions for the photolysis of H₂CO → H + HCO in the triplet threshold region, specifically for several rotational states in the 2²4³ and 2³4¹ H₂CO vibrational states that lie in this region. We have combined the strengths of two complementary techniques, laser-induced fluorescence for fine resolution and H atom Rydberg tagging for the overall distribution, to quantify the υ, N, and K_a distributions of the HCO photofragment formed via the singlet and triplet dissociation mechanisms. Both techniques are in quantitative agreement where they overlap and provide calibration or benchmarks that permit extension of the results beyond that possible by each technique on its own. In general agreement with previous studies, broad N and K_a distributions are attributed to reaction on the S₀ surface, while narrower distributions are associated with reaction on T₁. The broad N and K_a distributions are modeled well by phase space theory. The narrower N and K_a distributions are in good agreement with previous quasi-classical trajectory calculations on the T₁ surface. The two techniques are combined to provide quantitative vibrational populations for each initial H₂CO vibrational state. For dissociation via the 2³4¹ state, the average product vibrational energy (15% of E_avail) was found to be about half of the rotational energy (30% of E_avail), independent of the initial H₂CO rotational state, irrespective of the singlet or triplet mechanism. For dissociation via the 2²4³ state, the rotational excitation remained about 30% of E_avail, but the vibrational excitation was reduced.