主講人： 郭哲來研究員 (中央研究院原子與分子科學研究所)
題目：Linking Potential Energy Surface and Vibrational Spectroscopy via Ab Initio Anharmonic Algorithms
The potential energy surface (PES) of molecular systems plays a central role in chemistry. Vibrational spectroscopy methods traditionally serve as one of the major channels for Chemists to obtain information on the curvature of PES near a given stable minimum. Realistic molecular systems, however, are intrinsically anharmonic due to the existence of high-order terms in the PES. For example, vibrational (IR and Raman) spectra of many organic systems often reveal complex vibrational features near 3 μm which cannot be accounted for by harmonic approximation. Furthermore, these high-order terms of PES give rise to many important phenomena such as intramolecular vibrational energy redistribution (IVR). Vibrational modes associated with CH, NH, and OH bonds pose larger amplitude motions; the anharmonic effects thus can be quite substantial. In this perspective, we will focus on recent developments and applications of ab initio anharmonic algorithms, which not only help us understand vibrational spectra of important functional groups containing CH, NH, and OH but also provide a new window to see through PES beyond harmonic approximations. Through these theoretical analyses, we can link PES that theoreticians can compute directly to experimental observables collected via various vibrational spectroscopies. The examples discussed here were drawn mainly from recent gas-phase studies, yet the same notions can be applied to macro-molecular systems and condensed phases as well.