When does absorption occur in infrared spectroscopy?

A. When the frequency of the infrared radiation is the same as the rotational frequency of the bond
B. When the frequency of the infrared radiation is less than the frequency of the bond
C. When the frequency of the infrared radiation is the same as the vibrational frequency of the bond
D. When the frequency of the infrared radiation is slightly greater than the frequency of the bond

I think it's D, but I'm not sure. Help?

2 answers

Think on C.

thanks!!