Ultraviolet Photolysis of HCHO: Absolute HCO Quantum Yields by Direct Detection of the HCO Radical Photoproduct
Ultraviolet Photolysis of HCHO: Absolute HCO Quantum Yields by Direct Detection of the HCO Radical Photoproduct
复制标题
DOI：
10.1021/jp8070508
复制
发表时间：
2008-12-04
影响因子：
2.9
通讯作者：
Orr-Ewing, Andrew J.
中科院分区：
文献类型：
--
作者：
Carbajo, Paula Gorrotxategi;Smith, Shona C.;Orr-Ewing, Andrew J.
绝对量子产率的自由基（H + HCO）通道的甲醛光解，Phi（HCO），已被测量对流层相关的波长范围（λ）在300和330 nm之间。HCO光产物直接检测使用定制的，结合紫外（UV）吸收和腔衰荡（CRD）检测光谱仪。该仪器以前用于高分辨率（光谱分辨率类似于0.0035 nm）测量HCHO、西格玛（HCHO）（λ）和相对HCO量子产率的吸收截面。绝对Phi（HCO）值在7个波长，λ = 303.70，305.13，308.87，314.31，320.67，325.59，和329.51 nm，使用一个独立的校准技术的基础上同时UV光解的甲醛和Cl-2。这些Phi（HCO）测量显示出比当前NASA-JPL推荐的Phi（HCO）更大的可变性。绝对Phi（HCO）（λ）测定和先前测量的σ（HCHO）（λ）用于缩放一组广泛的相对HCO产率测量。该程序的结果是绝对自由基量子产率和HCHO吸收截面的乘积Phi（HCO）（lambda）sigma（HCHO）（lambda）在302.6至331.0 nm波长处的全套数据，波长分辨率为0.005 nm。该产品的光化学参数与高分辨率的太阳光子通量数据相结合，以计算HCHO的自由基（H + HCO）通道，J（HCO）的综合光解速率。与最新的NASA-JPL建议相比，在1 nm波长分辨率下报告的J（HCO）在0度太阳天顶角（SZA）增加了25%，在高SZA（80度）增加了33%。计算的光解速率与目前的HCHO数据相比的差异产生，部分原因是由于目前的数据集的波长分辨率较高，并突出了使用高分辨率光谱技术来实现完整和准确的HCHO光解过程的重要性。所有实验Phi（HCO）（lambda）sigma（HCHO）（lambda）数据可用于波长范围302.6-331.0 nm（在294和245 K下，在200 Torr的N-2浴气下）作为支持信息，波长分辨率为0.005、0.1和1.0 nm。还提供了0.1和1.0 nm分辨率的分子（H-2 + CO）光碎裂通道的Phi（H2+ CO）（lambda）sigma（HCHO）（lambda）等效数据集，该数据集使用测量的Phi（HCO）（lambda）sigma（HCHO）（tau）值生成。
Absolute quantum yields for the radical (H + HCO) channel of HCHO photolysis, Phi(HCO), have been measured for the tropospherically relevant range of wavelengths (lambda) between 300 and 330 nm. The HCO photoproduct was directly detected by using a custom-built, combined ultra-violet (UV) absorption and cavity ring down (CRD) detection spectrometer. This instrument was previously employed for high-resolution (spectral resolution similar to 0.0035 nm) measurements of absorption cross-sections of HCHO, sigma(HCHO)(lambda), and relative HCO quantum yields. Absolute Phi(HCO) values were measured at seven wavelengths, lambda = 303.70, 305.13, 308.87, 314.31, 320.67, 325.59, and 329.51 nm, using an independent calibration technique based on the simultaneous UV photolysis of HCHO and Cl-2. These Phi(HCO) measurements display greater variability as a function of wavelength than the current NASA-JPL recommendations for Phi(HCO). The absolute Phi(HCO)(lambda) determinations and previously measured sigma(HCHO)(lambda) were used to scale an extensive set of relative HCO yield measurements. The outcome of this procedure is a full suite of data for the product of the absolute radical quantum yield and HCHO absorption cross-section, Phi(HCO)(lambda)sigma(HCHO)(lambda), at wavelengths from 302.6 to 331.0 nm with a wavelength resolution of 0.005 nm. This product of photochemical parameters is combined with high-resolution solar photon flux data to calculate the integrated photolysis rate of HCHO to the radical (H + HCO) channel, J(HCO). Comparison with the latest NASA-JPL recommendations, reported at I nm wavelength resolution, suggests an increased J(HCO) of 25% at 0 degrees solar zenith angle (SZA) increasing to 33% at high SZA (80 degrees). The differences in the calculated photolysis rate compared with the current HCHO data arise, in part, from the higher wavelength resolution of the current data set and highlight the importance of using high-resolution spectroscopic techniques to achieve a complete and accurate picture of HCHO photodissociation processes. All experimental Phi(HCO)(lambda)sigma(HCHO)(lambda) data are available for the wavelength range 302.6-331.0 nm (at 294 and 245 K and under 200 Torr of N-2 bath gas) as Supporting Information with wavelength resolutions of 0.005, 0.1, and 1.0 nm. Equivalent data sets of Phi(H2+CO)(lambda)sigma(HCHO)(lambda) for the molecular (H-2 + CO) photofragmentation channel, produced using the measured Phi(HCO)(lambda) sigma(HCHO)(tau) values, are also provided at 0.1 and 1.0 nm resolution.