CHEM 524
-- Course Outline (Sect.
2)
II. Light Sources (alternate
reading: Oriel hand out )
Conventional-incandescent and discharge vs. laser-coherent Figure S-0
A. Black body sources follow Planck
result qualitatively Table S-1
Background -- ideal: emission-absorption
equilibrium
--constant energy density
(Text:
Fig 4-1) Figure
S-1
Planck: ------ Stefan-Boltzmann: -------- Wien:
, 
, 
Higher temperature—maximum moves to vis-uv, intensity increase
at all
Real sources -- correct for emissivity, transmittance (
Text
Fig 4-3) Figure
S-2,
—gray body
Incandescent
sources -- Continuum, continuous,
(Text Table 4-2, Fig 4-5,
4-4) - Compare to Black Body--Figure S-2,
Ceramic coated wire- Cheap, (~1000K)
SiC Glower (Glowbar)- higher power, cooling required (1300-1500K) --
good for FTIR – cross-section like aperture - Compare to Nerst: Figure S-3,
Nernst Glower-
expensive, fragile, high temperature (~1500->2000 K) Compare to Glowbar:
Figure S-3,
--special circuit (negative coefficient of resistance), --good for dispersive,
high resolution
C-Rod – cheap source, expensive housing, big power (KW), (Tc~2500
K) -- need inert atmosphere, good for IR with salt window
W-I lamp
– inexpensive, wide variety of designs and powers (T~2500+ K) -- good
for near IR, vis (typical source in commercial absorb. spectrometers)
B. Discharge
sources , Compare to Black Body: again,
also see, Figure S-4,
Figure S-5,
1. Continuum—high pressure
- --C-arc–old, stability problem, no window
- --Xe-arc (include Xe-Hg and Hg) (Ar arc)– popular, quartz envelope
(T~6000K)
- –Hg makes intense uv, vis lines
- –Ar common for CD, fluorescence, –good for vuv, not common
- --H2/D2 discharge lamp –low power, good
in uv, 370-180 (envelope) nm
2. Line sources– low pressure discharge-
get atomic/ion lines
- Na – lamp [a ]D
determination, ORD
- Hg – lamp–few uv vis lines (254nm max)–germacidal/fluorescence
excite
- Hollow cathode–AA source, select analyte
- Electrodeless discharge–more intense–atomic emission
3. Standards
- Intensity -- W-I and others (NIST calibrate)
- Frequency -- atomic: Hg (simple), hollow cathode: Fe/Th (vis), Ne (red)
C. Synchrotron
-- different mechanism
- experiment and operator must go to the source, especially inconvenient
- unique virtues: tunable, collimated, polarized, intense – especially
useful for uv,vuv
x-ray
