Define the term OVERTONE?

Question

ans w.r.t to chemistry

Answer 1

I have never heard overtone used with reference to Chemistry and found no definitions for that usage.  Here is a usage that I found.  maybe you can tell from that:

Objectives. In a collaboration between experiment (Prof. V. Vaida) and theory (Prof. R. Skodje) we propose to investigate a new paradigm for sun light initiated chemical reactions occurring by low energy by excitation of vibrational overtones in the ground electronic state.