Chapter 7 Flashcards
Why must the slit width of a prism monochromator be varied to provide constant effective bandwidths but a nearly constant slit width provides constant bandwidth with a grating monochromator? G d t l o a f f p, p d o a c f p.
G d t l o a f f p, p d o a c f p. Gratings disperse the light on a flat focal plane, prisms disperse onto a curve focal plane.
Why do quantitative and qualitative analyses often require different monochromator slit widths? Q r s (w s, m l), w q r r (n s).
Q r s (w s, m l), w q r r (n s). Quantitative requires sensitivity (wide slits, more light), while qualitative requires resolution (narrow slits).
Contrast spontaneous and stimulated emission S e - b t p i r a c o i a d, t r i i. S e - t p p a i p w t s t e, a c r i t r.
S e - b t p i r a c o i a d, t r i i. S e - t p p a i p w t s t e, a c r i t r. Spontaneous emission - because the process is random and can occur in any direction, the radiation is incoherent. Stimulated emission - the photons produced are in phase with those stimulating the emission, and coherent radiation is the result.
Define the term effective bandwidth of a filter. T e b o a f i t w i w u o t b t b t f w m a o-h t p h.
T e b o a f i t w i w u o t b t b t f w m a o-h t p h. The effective bandwidth of a filter is the width in wavelength units of the band transmitted by the filter when measured at one-half the peak height.
Why is glass better than fused silica as a prism construction material for a monochromator to be used in the region of 400 to 8OO nm? T d o 4 n t 8 n r, i w i a g p m t i a f s p m.
T d o 4 n t 8 n r, i w i a g p m t i a f s p m. The dispersion of 400 nm to 800 nm radiation is wider in a glass prism monochromator than in a fused silica prism monochromator.
For a grating, how many lines per millimeter would be required for the first-order diffraction line for A = 400nm to he observed at a reflection angle of 5° when the angle of incidence is 45°?
Consider an infrared grating with 84.0 lines per millimeter and 15.0 mm of illuminated area. Calculate the first-order resolution (λ/∆λ) of this grating. How far apart(in cm-1) must two lines centered at 1200cm-1 be if they are to be resolved?
The resolution of a monochromator given by R = λ/ Δλ= nN. For this example, n = 1 (first order), N= 15 mm x 84 lines/mm = 1260, so R = 1260. If λ= 1200 cm-1, Δλ = λ/R or 1200 cm-1/1260 or 0.952 cm-1. The lines at 1200 cm-1 must be 0.951 cm-1 apart to be resolved.
A monochromator has a focal length of 1.6 m and a collimating mirror with a diameter of 3.5 cm. The dispersing device was a grating with 1500 lines/mm. For first-order diffraction, (a) what is the resolving power of the monochromator if a collimated beam illuminated 3.0 cm of the grating? (b) what are the first- and second-order reciprocal linear dispersions of the monochromator?
