We studied the vibrational energy relaxation mechanisms of the amide I and amide II modes of N-methylacetamide (NMA) monomers dissolved in bromoform using polarization-resolved femtosecond two-color vibrational spectroscopy. The results show that the excited amide I vibration transfers its excitation energy to the amide II vibration with a time constant of 8.3 ± 1 ps. In addition to this energy exchange process, we observe that the excited amide I and amide II vibrations both relax to a final thermal state. For the amide I mode this latter process dominates the vibrational relaxation of this mode. We find that the vibrational relaxation of the amide I mode depends on frequency which can be well explained from the presence of two subbands with different vibrational lifetimes (∼ 1.1 ps on the low frequency side and ∼ 2.7 ps on the high frequency side) in the amide I absorption spectrum.

J. Chem. Phys.
Ultrafast Spectroscopy

Piatkowski, L., & Bakker, H. (2012). Vibrational relaxation pathways of amide I and amide II modes in N-methylacetamide. J. Chem. Phys., 136(16, Article number: 164504), 1–8. doi:10.1063/1.4705120