Answer to Question #113852 in Physical Chemistry for DEEPAK SINGH

Question

how many fundamental vibrational frequencies would you expect for Co2? how to you represent that modes?

Answer 1

As carbon dioxide is a linear molecule of three atoms, we need the 3N - 5 formula to determine how many vibrational modes it has. Plugging in '3' gives us four vibrational modes. Two of these modes are degenerate and correspond to different directions that are indistinguishable. Looking at the molecule, we find that stretching and bending vibrations can occur, and some of these movements do change the dipole moment of the molecule. The set of vibrational modes for CO2 is:

Asymmetrical C=O stretch with a wavenumber of 2351/cm.

Symmetrical C=O stretch with a wavenumber of 1332/cm.

Two C=O bending modes with a wavenumber of 671/cm, each moving along the x- and y-directions.