The intensity of the infrared IR spectrum produced by a molecule changes when the molecule undergoes a bond vibration due to the change in the molecule's dipole moment. Infrared spectroscopy is based on the absorption of infrared radiation by molecules, which leads to changes in their vibrational and rotational energy levels. When a molecule undergoes a bond vibration, its atoms move relative to each other, causing a change in the distribution of electron density within the molecule. This results in a change in the molecule's dipole moment, which is a measure of the separation of positive and negative charges within the molecule. The change in dipole moment during the vibration allows the molecule to interact with the electric field of the infrared radiation, leading to the absorption of energy and a transition to a higher energy level.The intensity of the IR spectrum depends on the magnitude of the change in the dipole moment during the vibration. If the change in dipole moment is significant, the molecule will absorb more infrared radiation, and the intensity of the corresponding peak in the IR spectrum will be higher. Conversely, if the change in dipole moment is small, the molecule will absorb less infrared radiation, and the intensity of the peak will be lower.It is important to note that not all bond vibrations result in a change in the dipole moment. Symmetric vibrations, such as the stretching of a triple bond in a linear molecule, do not cause a change in the dipole moment and are therefore not observed in the IR spectrum. These vibrations are said to be infrared inactive. In contrast, asymmetric vibrations, which do cause a change in the dipole moment, are infrared active and can be observed in the IR spectrum.