Ultrafast Spectroscopy, AMOLF, Science Park 104, Amsterdam 1098XG, Netherlands.
J Phys Chem B. 2023 May 25;127(20):4544-4553. doi: 10.1021/acs.jpcb.2c08992. Epub 2023 Mar 14.
The carboxylate anion group plays an important role in many (bio)chemical systems and polymeric materials. In this work, we study the orientation of carboxylate anions with various aliphatic and aromatic substituents at the water-air interface by probing the carboxylate stretch vibrations with heterodyne-detected vibrational sum-frequency generation spectroscopy in different polarization configurations. We find that carboxylate groups with small aliphatic substituents show a large tilt angle with respect to the surface normal and that this angle decreases with increasing size of the substituent. We further use the information about the orientation of the carboxylate group to determine the hyperpolarizability components of this group.
羧酸根阴离子在许多（生物）化学体系和聚合材料中起着重要作用。在这项工作中，我们通过在不同的偏振配置下用异频探测振动和频产生光谱探测羧酸伸缩振动，研究了在水-空气界面处具有不同脂肪族和芳香族取代基的羧酸根阴离子的取向。我们发现，具有小脂肪族取代基的羧酸根基团相对于表面法线有很大的倾斜角，并且这个角度随着取代基的增大而减小。我们进一步利用羧酸根基团取向的信息来确定这个基团的超极化率分量。
