共查询到19条相似文献,搜索用时 359 毫秒
1.
引言化学露光计是用来测定光强的光化学反应体系,一种好的露光计在一定的波长下,其量子产率是完全确定的。本文应用已知的草酸铁钾露光计标定光强,藉以测定偶氮苯光异构化反应的量子产率。早在1957年Zimmerman等人首次提出偶氮苯可以作为露光计,继而,在1976年Gauglitz 用动力学方法直接测得其量子产率。我们的工作是在吸收了Gauglitz方法优点的基础上,对偶氮苯光异构化反应量子产率的测定方法加以改进,将计算机的作用从简单计算扩大到对动力学经验方程的拟合,从而简化了实验操作,并能获得比较 相似文献
2.
3.
农药光解平均波长量子产率的测定 总被引:6,自引:0,他引:6
本文报道一种以高压汞灯复合光为光源测定农药平均波长量子产率的方法。该方法的光最计为草酸铁钾,通过光量计测得光源的照射强度。以气相色谱分析农药降解的残余浓度求得反应速率常数,用紫外分光光度计测定农药在确定波长下的摩尔吸光系数,并与该波长光强相乘进行积分,计算出十二种农药的平均波长Φ。本法所得结果更接近于自然光下的结果,更适合应用于实际环境中。 相似文献
4.
萤光量子产率对于电子激发态的构造和能量转移机构的研究极为重要。普通是以适当的物质作基准而测定量子产率相对值。但是可信赖的基准物质为数不多,选择不当可能造成颇大的误差等等,使量子产率的测定出现许多的问题。然而现在有了一个萤光量子产率的绝对测定法,即量热法(J. Olmsted, Ⅲ, J. Phys. Chem., 83, 2581(1979)). 相似文献
5.
6.
7.
本文研究了由偏二氯乙烯-丙烯酸甲酯共聚合物(VdCl2-MA)和五甲氧基红指示剂组成的酸敏变色记录材料的光谱特性,测定了其光分解量子产率.通过添加光敏剂使原来只有在254nm紫外光下曝光才能发生光分解反应的酸敏变色材料在35nm紫外光下曝光也可发生光分解而变色.酸敏变色材料在254nm处紫外光曝光量子产率为0.032-0.020;在35nm处紫外光曝光量子产率为0.110-0.034.光敏剂的加入使酸敏变色材料量子产率提高了2-4倍. 相似文献
8.
9.
10.
近年来,鎓盐化合物,如碘鎓盐、硫鎓盐和氧鎓盐等,作为光引发剂在酸催化微电子器件加工技术中得到了广泛的应用。我们曾对它们的稳态和瞬态光解及机理进行过比较详细的研究,也发现它们在光解时能以不同途径生成很强的无机酸(Bronsted酸),进而可引发单体阳离子聚合或高分子薄膜的交联等。很显然,在这一工作中准确测定它们光解时生成酸的量子产率将与微电子器件加工中光刻质量(如分辨率等)密切相关。在过去的工作中,一般采用酸碱滴定法困,即用氢氧化钠,氢氧化钾水溶液测定嗡盐光解生成酸的量子产率,但由于嗡盐在水中溶解度不很理想,因而结果往往不能重复,测定的酸量子产率误差较大,如Pappas用此法测得的三苯基硫嗡盐在254 nm光解生成酸量子产率为0.74,误差在正负20%。 相似文献
11.
The absolute yield of bacteriochlorophyll fluorescence in vivo 总被引:4,自引:0,他引:4
Abstract— –The method of Weber and Teale for determining absolute fluorescence quantum yield of dyes in solution was modified for determination of the yield of bacteriochlorophyll fluorescence from chromatophores and whole cells of photosynthetic bacteria. Measured yields ranged from about 1–6 per cent. The yield depended on intensity and wavelength of the exciting light. The higher yield at higher light intensity was interpreted as due to saturation of photosynthesis. The lower yield in some strains when excited at 810 nm was attributed to preferential excitation of the reaction center pigment P800. From this study and the lifetime measurements of others, the relation τ=Q.τ0 was substantiated for the fluorescence of bacteriochlorophyll in vivo, τ being the actual lifetime, τ0 the intrinsic lifetime as estimated from the absorption band area, and Q the quantum yield of fluorescence. 相似文献
12.
Abstract— It is known that thymine forms dimers when aqueous solutions are irradiated with ultraviolet light while in the frozen state, but does not form dimers when solutions are irradiated in the liquid state. The eutectic point of aqueous thymine solutions was found to be. —0.02°C. Since the irradiation of frozen solutions is always carried out at lower temperatures, the dimerization must be occurring in the solid state. Activation energies and quantum yields for dimer formation were determined by irradiating 1–mm layers of thymine solution at —5°C to — 707deg;C for various lengths of time. As expected, the activation energy was zero. After measuring the amount of radiation scattered by samples of ice, the extreme values for the quantum yield were found to be 0.73 and 4.08. The lower limit assumed that all the scattered light was absorbed by thymine; the upper limit assumed that none was absorbed. Since the theoretical maximum quantum yield is 2, the best estimate of the quantum yield is considered to be between 1 and 2. 相似文献
13.
Abstract The short-term adaptation of intact leaves to an increase in light intensity was studied by an analysis of chlorophyll fluorescence and oxygen evolution monitored by photoacoustics. An increase in light intensity led to an oxygen “gush”. This “gush” was followed by a large (up to 120%) biphasic increase in the yield of oxygen evolution characterized by a fast phase (T = 0.5–2 min) and a slow phase (T = 4–20 min). The fast phase of the increase in oxygen yield was coupled to a decrease of fluorescence, whereas the slow phase was accompanied by a parallel fluorescence increase. A comparison of fluorescence parameters with oxygen yield indicates that the slow phase of the increase in oxygen yield was coupled to an increase in the antenna size of photosystem II. The slow phase was not inhibited by the uncoupler Nigericin but it was absent in chlorophyll-b-less barley mutants dencient in the light harvesting chlorophyll a/b protein complex of photosystem II (LHC II). These experiments indicate that changes in the LHC II mediated energy distribution, which occur in the time-range of several minutes, are involved in the adaptation to changing light intensities. Moreover, electrophoretic analysis of 32P orthophosphate labeled leaf discs adapted to low and high light intensities suggests that the slow phase of the increase in oxygen evolution involves dephosphorylation of the 25 kDa polypeptide of LHC II, by a small extent of 12%. The trigger for the slow phase of the increase in oxygen yield does not involve the oxidation of the plastoquinone pool. It was found that in response to the increased light intensity, the plastoquinone pool became more reduced as judged by model calculations. Experiments with the uncoupler Nigericin suggest that the control of the slow phase of adaptation to increased light intensity was also not exerted by the pH gradient across the thylakoid membrane. The similarities between the adaptation to increased light intensity and the state II to state I transition suggest that both adaptation phenomena involve LHC II dephosphorylation possibly triggered by the cytochrome b6/f complex. 相似文献
14.
Abstract— The short-term adaptation of intact leaves to an increase in light intensity was studied by an analysis of chlorophyll fluorescence and oxygen evolution monitored by photoacoustics. An increase in light intensity led to an oxygen “gush”. This “gush” was followed by a large (up to 120%) biphasic increase in the yield of oxygen evolution characterized by a fast phase (T = 0.5–2 min) and a slow phase (T = 4–20 min). The fast phase of the increase in oxygen yield was coupled to a decrease of fluorescence, whereas the slow phase was accompanied by a parallel fluorescence increase. A comparison of fluorescence parameters with oxygen yield indicates that the slow phase of the increase in oxygen yield was coupled to an increase in the antenna size of photosystem II. The slow phase was not inhibited by the uncoupler Nigericin but it was absent in chlorophyll-b-less barley mutants deñcient in the light harvesting chlorophyll a/b protein complex of photosystem II (LHC II). These experiments indicate that changes in the LHC II mediated energy distribution, which occur in the time-range of several minutes, are involved in the adaptation to changing light intensities. Moreover, electrophoretic analysis of 32P orthophosphate labeled leaf discs adapted to low and high light intensities suggests that the slow phase of the increase in oxygen evolution involves dephosphorylation of the 25 kDa polypeptide of LHC II, by a small extent of 12%. The trigger for the slow phase of the increase in oxygen yield does not involve the oxidation of the plastoquinone pool. It was found that in response to the increased light intensity, the plastoquinone pool became more reduced as judged by model calculations. Experiments with the uncoupler Nigericin suggest that the control of the slow phase of adaptation to increased light intensity was also not exerted by the pH gradient across the thylakoid membrane. The similarities between the adaptation to increased light intensity and the state II to state I transition suggest that both adaptation phenomena involve LHC II dephosphorylation possibly triggered by the cytochrome b6/f complex. 相似文献
15.
Jordan W. Greenberg Vinay Malhotra John F. Ennever 《Photochemistry and photobiology》1987,46(4):453-456
The quantum yield and the relative photochemical yield for lumirubin formation from bilirubin bound to human albumin were determined at eight wavelengths from 410 to 520 nm. The quantum yield averaged 0.0015 for irradiation between 450 and 490 nm. At 410 and 430 nm the quantum yield was slightly lower. At the long wavelength end of the absorption band, from 500 to 520 nm, the quantum yield averaged 0.003. The relative photochemical yield, normalized to constant fluence, was greatest at 500 nm. 相似文献
16.
S. P. Balashov E. S. Imasheva R. Govindjee T. G. Ebrey 《Photochemistry and photobiology》1991,54(6):955-961
The maximum photosteady state fraction of K, xKmax, and the ratio of the quantum yields of the forward and back light reactions, trans-bacteriorhodopsin (bR) hArr; K, φbR/φK, were obtained by measuring the absorption changes produced by illumination of frozen water-glycerol (1:2) suspensions of light-adapted purple membrane at different wavelengths at -165°C. An independent method based on the second derivative of the absorption spectrum in the region of the β-bands was also used. It was found that The quantum yield ratio (0.66 ± 0.06) was found to be independent of excitation wavelength within experimental error in the range510–610 nm. The calculated absorption spectrum of K has its maximum at603–606 nm and an extinction 0.85 ± 0.03 that of bR. At shorter wavelengths there are P-bands at 410, 354 and 336 rim. Using the data of Hurley et al. (Nature 270,540–542, 1977) on relative rates of rhodopsin bleaching and K formation, the quantum yield of K formation was determined to be 0.66 ± 0.04 at low temperature. The quantum efficiency of the back reaction was estimated to be 0.93 ± 0.07. These values of quantum efficiencies of the forward and back light reactions of bR at - 165°C coincide with those recently obtained at room temperature. This indicates that the quantum efficiencies of both forward and back light reactions of bacteriorhodopsin are temperature independent down to -165°C. 相似文献
17.
18.
B. Nathanson † M. Brody † S. Brody ‡ S. B. Broyde ‡ 《Photochemistry and photobiology》1967,6(3):177-187
Abstract— A detailed in vitro study was made of the flavin sensitized photoinactivation of indoleacetic acid, using primarily riboflavin as sensitizer. The dependence of the quantum yield on reactant concentrations, pH, presence of oxygen, viscosity, temperature, KI concentration, and solvent was determined. The involvement of a limiting dark reaction was demonstrated, using an intermittent light technique. The results are consistent with a mechanism involving a metastable state of riboflavin as the photochemically reactive species. The calculated rate constant for intersystem crossing to this state was found to be 2.5 times 108 /sec. Riboflavin, in the metastable state, is believed to oxidize indoleacetic acid to indolealdehyde, with subsequent recovery of riboflavin by autoxidation. The maximum quantum yield of the photoinactivation of IAA is 0.71, indicating a highly efficient process, approaching 100% when energy loss due to riboflavin fluorescence is taken into account. Both carotenoids and pure chlorophyll- a were found to be inactive as sensitizers. 相似文献
19.
DEPENDENCY OF APPARENT RELATIVE QUANTUM YIELD OF ISORHODOPSIN TO RHODOPSIN ON THE PHOTON DENSITY OF PICOSECOND LASER PULSE 总被引:2,自引:0,他引:2
Hideki Kandori Sinzi Matuoka Hiroshi Nagai Yoshinori Shichida Tôru Yoshizawa 《Photochemistry and photobiology》1988,48(1):93-97
Abstract— The quantum yield of bleaching of isorhodopsin relative to that of rhodopsin was measured by irradiation of both pigments with a steady light source or a picosecond laser pulse. The each pigment was prepared by incubation of 11- cis or 9 -cis retinal with opsin, respectively. The ratio of isorhodopsin to rhodopsin in the quantum yield was estimated to be 0.37 using irradiation with a steady light, while with a weak picosecond laser pulse (excitation photon density: below 20 μ.J/1.8 mmφ), it was estimated to be 0.39. Both values are in good agreement with each other. On the other hand, excitation with a strong picosecond laser pulse (above 20 μ.J/1.8 mmφ) produced a larger ratio than 0.39, indicating that saturation effects can be easily observed by irradiation with strong picosecond laser pulses. 相似文献