ESS 51 F2013 lecture 15 spectroscopy Watenphul

Examples h2o n 3 3 x 3 6 3 vibra6onal

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: : H2O N = 3 –> 3 x 3 – 6 = 3 vibra6onal modes stretching vibra6ons ν3 3756 cm–1 ν1 3652 cm–1 bending vibra6on ν2 1595 cm–1 Molecular vibra6ons A molecule of N atoms has 3N degrees of freedom. The number of vibra6onal modes is given by 3N-­‐6, in case of a linear molecule 3N-­‐5. Examples: CO2 N = 3 –> 3 x 3 – 5 = 4 vibra6onal modes stretching vibra6ons ν3 2349 cm–1 bending vibra6ons ν2 667 cm–1 ν2 667 cm–1 Molecular vibra6ons A molecule of N atoms has 3N degrees of freedom. The number of vibra6onal modes is given by 3N-­‐6, in case of a linear molecule 3N-­‐5. Examples: CO2 N = 3 –> 3 x 3 – 5 = 4 vibra6onal modes stretching vibra6ons ν3 2349 cm–1 bending vibra6ons ν2 667 cm–1 degenera6on ν2 667 cm–1 Molecular vibra6ons A molecule of N atoms has 3N degrees of freedom. The number of vibra6onal modes is given by 3N-­‐6, in case of a linear molecule 3N-­‐5. Examples: CO2 N = 3 –> 3 x 3 – 5 = 4 vibra6onal modes stretching vibra6ons not IR ac6ve ν3 2349 cm–1 bending vibra6ons ν2 667 cm–1 ν2 667 cm–1 Selec6on rule Vibra6ons are IR ac6ve, if the dipole moment μ of the vibra6ng molecule periodically changes due to the oscilla6on of the atoms. Vibra6ons are Raman ac6ve, if the polarisability α of the vibra6ng molecule periodically changes due to the oscilla6on of the atoms. Infrared (IR) spectroscopy IR spectra show the absorbance of the sample as func6on of the radia6on frequency (in cm–1). The transmi?ance T is defined by the ra6o of the intensity of the transmi?ed light IIR to the intensity of the incident light I0 T = IIR / I0. detector IR source Infrared (IR) spectroscopy The transmi?ance T is defined by the ra...
View Full Document

This document was uploaded on 04/03/2014.

Ask a homework question - tutors are online