C566lecture13_000

C566lecture13_000 - C566 Master Lecture Notes Weeks 5 - 8...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
C566 Master Lecture Notes Weeks 5 - 8 IR spectroscopy done in interesting ways Old-fashioned measurements- direct absorption from a broad-band source, have limitations. dI = -  N I dz dI/I = -  N dz -ln I /I o = A =  N =  [sample] For systems with necessarily low number densities (reactive species, low vapor pressure species, etc) absorption can be very low, and very clever strategies have been devised to mke these measurments. 1. “Detection of the hydronium ion (H 3 O + ) by high resolution infrared spectroscopy,” M.H. Begemann, C.S. Gudeman, J. Pfaff, and R.J. Saykally, Phys. Rev. Lett. 51 , 554 (1983). Signal from H 3 O + was discerned from the 10 4 times more abundant H 2 O in the ion source using velocity modulated absorption spectroscopy. To understand the principle of this technique, please read the section in your text on Doppler broadening (pp 35-36 in the 4 th Ed.). Before the technique was developed, it was very difficult to measure the absorption spectra of ions, since they are typically found at much lower number densities than associated neutrals, so any contribution to the spectrum of the sample is microscopic. Light source Sample, length = ; [sample] or number density, N Monochromator (dispersing element) Detector/ recorder
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Several sources of finite linewidths in spectroscopic measurements (see chapter 2.Section 3 in Hollas): A. Lifetime broadening-- E t /2 If the excited state lifetime is 10 8 seconds, E = /2 10 -8 = 3.3x10 -11 cm -1 s/4pi 10 -8 = 3x10 -4 cm -1 ~ 8 MHz. 2 t looks like 1/k = in first order kinetics treatment; kt dt dN B. Doppler Broadening- 1-dimensional velocity distribution n(v) dv = dv e kT m kT mv 2 2 / 1 2 2 o 2  = 2 E/ h
Background image of page 2
 c s c s c s receding 1
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

C566lecture13_000 - C566 Master Lecture Notes Weeks 5 - 8...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online