Multidimensional Spectral Fingerprints of a New Family of Coherent Analytical Spectroscopies

Abstract

Triply resonant sum frequency (TRSF) and doubly vibrationally enhanced (DOVE) spectroscopies are examples of a recently developed family of coherent multidimensional spectroscopies (CMDS) that are analogous to multidimensional NMR and current analytical spectroscopies. CMDS methods are particularly promising for analytical applications because their inherent selectivity makes them applicable to complex samples. Like NMR, they are based on creating quantum mechanical superposition states that are fully coherent and lack intermediate quantum state populations that cause quenching or other relaxation effects. Instead of the nuclear spin states of NMR, their multidimensional spectral fingerprints result from creating quantum mechanical mixtures of vibrational and electronic states. Vibrational states provide spectral selectivity, and electronic states provide large signal enhancements. This paper presents the first electronically resonant DOVE spectra and demonstrates the capabilities for analytical chemistry applications by comparing electronically resonant TRSF and DOVE spectra with each other and with infrared absorption and resonance Raman spectra using a Styryl 9 M dye as a model system. The methods each use two infrared absorption transitions and a resonant Raman transition to create a coherent output beam, but they differ in how they access the vibrational and electronic states and the frequency of their output signal. Just as FTIR, UV-vis, Raman, and resonance Raman are complementary methods, TRSF and DOVE methods are complementary to coherent Raman methods such as coherent anti-Stokes Raman spectroscopy (CARS).

WrightTools: a Python package for multidimensional spectroscopy

“…The typical spectroscopist only really cares about a small subset of these variables, but exactly what subset matters may change as different strategies are used to explore the dataset. Furthermore, it is often useful to "combine" multiple variables using simple algebraic relationships to exploit the natural symmetry of many MDS experiments and to draw comparisons between different members of the MDS family (Neff-Mallon & Wright, 2017). In light of these details, WrightTools provides a high-level Axis class that allows users to transparently define which variables, variable relationships, and unit conventions are important to them for representation and manipulation.…”

“…WrightTools has directly enabled no fewer than eleven publications (Chen et al, 2017;Czech et al, 2015;Horak et al, 2018;Kohler, Thompson, & Wright, 2017Morrow, Kohler, & Wright, 2017;Morrow, Kohler, Czech, & Wright, 2018;Neff-Mallon & Wright, 2017;. Many of these publications have associated open datasets and WrightTools-based processing scripts which enhance the scientific community's ability to audit and reproduce the published work.…”

Triple sum frequency pump-probe spectroscopy of transition metal dichalcogenides

“…The selectivity of TSF is due to the increase in output intensity * wright@chem.wisc.edu achieved when the driving fields are resonant with multiple states; the multiple resonance conditions act as a "fingerprint". [20] TSF has been used to investigate vibrational and electronic coupling in molecules, [21][22][23][24][25][26] and recently, TSF has revealed the electronic states of MoS 2 and the mixed-vibrational-electronic coupling of organicinorganic perovskites. [27,28] In this paper, we measure the pump-TSF-probe response of MoS 2 and WS 2 , which are layered semiconductors in the TMDC family.…”

Communication: Multidimensional triple sum-frequency spectroscopy of MoS2 and comparisons with absorption and second harmonic generation spectroscopies

“…The polarization is expressed as an expansion in electric field and susceptibility (χ) order. Absorption, SHG, and TSF (THG) depend on χ (1) , χ (2) , and χ (3) , respectively. Absorption is proportional to Im χ (1) .…”

“…The additional detuning factors are defined by ∆ 123 gck ≡ ω cgk − ω 321 − iΓ and ∆ 12 gbk ≡ ω bgk − ω 21 − iΓ in which ω ab is the frequency difference between bands a and b at point k in the BZ. The JDOS formalism employed in Equation 2 can be abstracted to describe χ (2) and χ (3) with the introduction of multidimensional joint density functions. These joint densities depend not just on the energy difference between the initial and final states, but also on the energy differences between the intermediate states reached during the sum-frequency process.…”