# FIU CHM 4130 - Key_for Chapter_ 7 (3 pages)

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## Key_for Chapter_ 7

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- Pages:
- 3
- School:
- Florida International University
- Course:
- Chm 4130 - Instrumental Analysis

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CHAPTER 7 Equation 7 17 can be written w Oeff D 1 For a prism monochromator the linear 7 1 CHAPTER 7 dispersion D decreases continuously with increasing wavelength The reciprocal linear dispersion D 1 thus increases as the wavelength becomes longer Hence if Oeff is to 7 1 Equation 7 17 can be written w eff D 1 For a prism monochromator the linear dispersion D decreases withbeincreasing remain constant w thecontinuously slit width must decreasedwavelength accordingly The Forreciprocal a gratinglinear dispersion D 1 thus increases as the wavelength becomes longer Hence if eff is to remain constant w essentially the slit width must over be decreased accordingly For a range gratingThus w instrument D 1 is constant a considerable wavelength instrument D 1 is essentially constant over a considerable wavelength range Thus w does doesnot notneed needtotobe bevaried variedwith withaagrating gratingmonochromator monochromator 7 2 For qualitative analysis it is important to resolve as many absorption bands as possible 7 2 For qualitative analysis it is important to resolve as many absorption bands as possible for identification purposes This consideration often that means slit widths for identification purposes This consideration often means slitthat widths should be as should be as narrow as possible On the other hand for quantitative methods better signal to noise ratios On andthe hence can bemethods obtained better with wider slit widths narrow as possible otherhigher hand precision for quantitative signal to noise ratios and hence higher precision can be obtained with wider slit widths 7 3 7 3 a Omax 2 90 u 103 T 2 90 u 103 5000 K 0 58 Pm or 580 nm b Omax 2 90 u 103 3000 K 0 967 Pm or 967 nm c Omax 2 90 u 103 1500 K 1 93 Pm 7 4 a Et DT4 5 69 u 10 8 W m 2 K 4 u 5000 K 4 3 56 u 107 W m 2 7 6 Spontaneous 8emission occurs when a4 species loses all or part of its excess energy 2 4 6 2 b E 5 69 u 10 W m K u 3000 K 4 61 u 10 W m t in the form of fluorescence or phosphorescence radiation Because the process is random and can occur in any direction the radiation is incoherent Stimulated emission is brought 5 5 69 u 10 8ofWexcited m 2 K 4species u 1500 K 4externally 2 88 u 10 W m 2photons that have c Eby t interaction about with produced energies exactly matching the energy of a transition The photons produced are in phase the 2 90 emission coherent radiation is the 7 5 with a those Omax stimulating 2 90 u 103 T u 103and 2870 1 01 Pm or 1010 nmresult Omax 2 90 u 103 3500 0 829 Pm or 829 nm 7 7 A four level laser system has the advantage that population inversion is achieved 6 4 necessary more system it is only b easily

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