χ⁽⁴⁾ Raman Spectroscopy for Buried Water Interfaces

Abstract

π‐Type H‐bonds that are not found in bulk liquid phases, where σ‐type H‐bonds prevail, were detected for the dye rhodamine 800 at air/water and fused silica/water interfaces (see picture) by interface‐selective fourth‐order nonlinear (χ(4)) Raman spectroscopy in the frequency domain. This new method allows vibrational spectra of organic solutes at liquid interfaces to be obtained in the whole fingerprint region (200–2800 cm−1).

Different Molecules Experience Different Polarities at the Air/Water Interface

“…Recently, we have developed multiplex electronic sum frequency generation (ESFG) spectroscopy ( Figure 1), in which a narrowband near-IR laser pulse (w 1 ) and a broadband white-light continuum (w 2 ) are irradiated on interfaces and the entire ESFG (w 1 + w 2 ) spectrum is detected with a multichannel detector in a single measurement [18][19][20][21] (see the Supporting Information for experimental details). This new second-order nonlinear spectroscopy technique provides precise and quantitative interfacial electronic spectra with an unprecedented high signal-to-noise ratio that is comparable to the absorption spectra of molecules in the bulk solutions.…”

“…ESFG spectroscopy enables us to intensively study the properties of molecules at liquid interfaces by electronic spectroscopy at the same level as for molecules in the bulk solutions. [18][19][20][21] Herein, we report a systematic study on solvatochromism at the air/water interface by using ESFG spectroscopy. This work clearly shows that the electronic spectra of a series of molecules exhibit significantly different solvatochromic shifts at the same air/water interface, thus demonstrating that different molecules experience different effective polarity at the air/water interface.…”

Novel interface‐selective even‐order nonlinear spectroscopy

“…Therefore, if the vibrational reswww.lpr-journal.org onance is achieved with only visible or NIR light, the above-mentioned problems are solved. Based on this idea, we recently developed the two types of the interfaceselective χ (4) Raman spectroscopy in the frequency domain [25,27], i.e., CARS-type homodyne-detection χ (4) Raman and inverse-Raman-type heterodyne-detection χ (4) Raman, in which the vibrational resonance is realized by the Raman process (CARS: coherent anti-Stokes Raman scattering [53][54][55][56][57][58][59]). Because χ (4) Raman does not employ IR but uses only visible or NIR light, it can be applied to interfaces buried in thick IR absorbers if they are transparent for visible or NIR light.…”

“…Recently, we developed new nonlinear spectroscopic methods, i.e., second-order electronic sum frequency generation (ESFG) and fourth-order nonlinear Raman (χ (4) Raman) spectroscopies [24][25][26][27]. They overcome the limitation of existing SHG and VSFG, and hence can extend the application of even-order spectroscopies.…”

Advantages of time-resolved difference X-ray solution scattering curves in analyzing solute molecular structure

“…Time-resolved scattering with either short-pulse X-rays [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] or electrons [19][20][21][22][23][24][25][26][27][28] offers a new and powerful molecular probe that is complementary to time-resolved optical spectroscopy [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], for monitoring structural changes of molecules in the course of a reaction. In a typical experiment [7-11, 13-16, 19, 22-27, 45-48], a sample containing the molecules of interest, is irradiated by an ultrashort optical pulse to initiate a reaction, and after a well-defined time delay, ultrashort X-ray/electron pulses are sent to the sample undergoing reaction processes and the scattered X-rays/electrons, which carry the structural information about the molecules at that time delay, are detected.…”