Incident photon flux, relationship

A. The number of photons required per oxygen evolved is derived from the initial linear part of the curve describing the relationship between incident photon flux density and oxygen evolution ... 

The relationship between the photocurrent and the incident photon flux is given by... 

Either 1 /(I qF ) (constant temperature and variable incident photon flux) or baIF (variable temperature and constant incident photon flux) can be used as the variable constraint. The photokinetic factor F must be measured for each of the photostationary states. It should be noted, however, that the relationship in Eq. (A2.1) comprises four unknown quantities (eg, eB, AB, and < >Ba) and cannot be analyzed directly as the numerical values of the slope p and the intercept i with the y axis produce values for only two unknown parameters (Figure A2). hi Section A2.2, we show how this can be resolved. 

Figure A2. Application of the steady-state relationship of Eq. (A.2.2.1) to extract eB and <))AB for a thermally reversible, photochromic AB, 1< >, 1 system. A plot of 1/( PS - eA) vs. 1/(/qF ) yields a straight line of slope p with an intercept along the y axis of i. Each experimental point corresponds to the observation of a photostationary state obtained at constant temperature for a given value of incident photon flux I a. This produces AB = 0.38.)...

Before photocurrent excitation spectra can be normalised to allow for the wavelength dependence of the illumination intensity, it is essential to establish the relation between the photocurrent response and the incident photon flux. This can be done using calibrated neutral density fdters. The relationship is generally not linear for photoconductive systems or for systems in which processes such as surface recombination or photocurrent multiplication occur (Peter, 1990). The incident photon flux can be measured using a UV-enhanced silicon photodiode with known sensitivity. 

From this expression, it is clear that the threshold pumping rate will be modified by the quenching rate through T32 alone. Also, it has been shown that the relationship between the pumping rate and the incident photon flux and the optical absorption of the CP film will remain the same in the presence of an analyte. 

Figure 8-19. Idealized hyperbolic relationship between the photosynthetic photon flux incident on the upper leaf surface and the net C02 uptake rate for a C3 plant. The intercept on the ordinate (y-axis) indicates the net COz flux by respiration in the dark (-1 pmol m-2 s 1), the intercept on the dashed line indicates the light compensation point (a PPF of 15 pmol m 2s l), the essentially linear initial slope (37co2 ppf) indicates the quantum yield (Eq. 4.16) for photosynthesis [(5 - 0 pmol m 2 s l)/(115 -15 pmol m-2 s l) = 0.05 mol C02/mol PPF], and the maximum Jco2reached asymptotically at high PPF indicates the light-saturated net C02 uptake rate (about 12 (xrnol m-2 s l often designated AmaK or Amax). Here the quantum yield is based on incident photons, but more appropriately it should be based on absorbed photons.

Figure 1.67. Intensity dependence of the correlation signal on a log-log scale with the optical electric field perpendicular to the chains for an applied voltage of 100 V The relationship is almost linear with a slope of 0.9. The maximum photon flux incident on the (CH) film was 2xl0 cm" where the values have been corrected for reflection and transmission. (Reprinted with permission from ref 149)...

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