کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9770213 | 1501942 | 2005 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Nuclear spin symmetry state relaxation in formaldehyde
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موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی آلی
پیش نمایش صفحه اول مقاله
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چکیده انگلیسی
New measurements of the rate constant of the ortho-para conversion in monomeric gaseous formaldehyde (H2CO) are presented. Separation of the nuclear spin isomers of formaldehyde was obtained by selective UV laser photolysis of ortho-formaldehyde in the natural ortho-para mixture. A first group of experiments is devoted to the question of surface relaxation. Measurements in low pressure formaldehyde gas show fast relaxation at very low pressures, falling to a minimum at pressures of about 1Â mbar and then rising linearly with pressure. The fast relaxation at very low pressures is interpreted as surface relaxation and this interpretation is confirmed by the fact that different wall materials of the fluorescence cells yield different relaxation constants. A second group of experiments extended the pressure range of the nuclear spin symmetry state relaxation measurements in formaldehyde by adding H2 or SF6 to it up to pressures of 1Â bar. The experimental data follow qualitatively the behaviour that is predicted by theory [R.F. Curl Jr, J.V.V. Kasper, K.S. Pitzer, J. Chem. Phys. 46 (1967) 3220]. Quantitative agreement with theory could be reached by taking calculated values of the spin-rotation coupling constants [P.L. Chapovsky, J. Mol. Struct. 599 (2001) 337] about 35% higher and using surprisingly large nuclear spin symmetry state relaxation cross-sections.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Molecular Structure - Volume 741, Issues 1â3, 2 May 2005, Pages 97-106
Journal: Journal of Molecular Structure - Volume 741, Issues 1â3, 2 May 2005, Pages 97-106
نویسندگان
Christian Bechtel, Elias Elias, Bernhard F. Schramm,