Question

a.) How many vibrational modes exist for CH2O? Sketch these. b.) How many unique (i.e., different) vibrational frequencies can be observed in CH2O c.) Which of the vibrational modes will show up in an infrared spectrum, and which in a Raman spectrum?

Answer 1

Here you go:

b) In this answer if the asked question is about the number of different frequencies present, then there are 6 types of different modes. 6 frequencies will be observed in the spectrum!

a) CH₂O or formaldehyde has 4 atoms in it. . and it is not a linear molecule, thus, the number of normal modes of vibrations 0 (BN-6), where I' is the no. of - atony. o 3x4-6012-626 Thus, there will be o vibrational modes and these are:- KHHy Red HA Symmetric C-H stretch fa) Crostro cauOS, 요 ca H out of plane a Asymmetric - Ch Rock (B2) Bend (B) (H str. (B2) b) As we can see there are namely '3' types of unique vibrations, A, B, B2. e) Since, this is not a centrosymmetric molecule they all IR active modes can be Ramon active. Thus, ALB, & B2 all will appear in IR as well as in Raman Speckun.