For one <normal mode>, the fundamental is $v=0\to1$, with other modes initially in their ground levels. In the linear-dipole <harmonic approximation>, the transition moment is nonzero for $\Delta v=\pm1$, so a <vibrational fundamental> is normally much stronger than its overtones, provided the mode has <vibrational infrared activity>.

Solution

Past exam of the chemistry A course of the University of Cambridge / 2025 / Paper 1 / A3 / a / i / Solution

 Solution (source code)