(ii)Pressure broadening: Collisions with atoms/molecules transfers small quantities of vibrational energy (heat)-ill-defined ground state energy Effect worse at high pressures For low pressure hollow cathode lamps(1-10 torr)10-1-10-2 A For high pressure Xe lamps(>10,000 torr)100-1000 A(turns lines into continua!) (iii)Doppler broadening Change in frequency produced by motion relative to detector In gas,broadens line symmetrically Doppler broadening increases with T ·At room T~10-2-10-3A Total linewidth typically 0.01-0.1 A CEM 333 page 7.6 (ii) Pressure broadening: Collisions with atoms/molecules transfers small quantities of vibrational energy (heat) - ill-defined ground state energy Effect worse at high pressures • For low pressure hollow cathode lamps (1-10 torr) 10-1-10-2 Å • For high pressure Xe lamps (>10,000 torr) 100-1000 Å (turns lines into continua!) (iii) Doppler broadening: Change in frequency produced by motion relative to detector In gas, broadens line symmetrically Doppler broadening increases with T • At room T ~10-2-10-3 Å Total linewidth typically 0.01-0.1 Å CEM 333 page 7.6