Abstract
Coherent two-dimensional (2D) optical spectroscopy has revolutionized our ability to probe many types of couplings and ultrafast dynamics in complex quantum systems. The dynamics and function of any quantum system strongly depend on couplings to the environment. Thus, studying coherent interactions for different environments remains a topic of tremendous interest. Here we introduce coherent 2D electronic mass spectrometry that allows 2D measurements on effusive molecular beams and thus on quantum systems with minimum system–bath interaction and employ this to identify the major ionization pathway of 3d Rydberg states in NO2. Furthermore, we present 2D spectra of multiphoton ionization, disclosing distinct differences in the nonlinear response functions leading to the ionization products. We also realize the equivalent of spectrally resolved transient-absorption measurements without the necessity for acquiring weak absorption changes. Using time-of-flight detection introduces cations as an observable, enabling the 2D spectroscopic study on isolated systems of photophysical and photochemical reactions.
Highlights
Coherent two-dimensional (2D) optical spectroscopy has revolutionized our ability to probe many types of couplings and ultrafast dynamics in complex quantum systems
Using time-of-flight mass spectrometry, we obtain a 2D spectrum simultaneously for the parent molecule and each of its fragments. With this implementation of 2D electronic spectroscopy, we exemplarily investigate ionization pathways in nitrogen dioxide (NO2) and acquire ion-selective 2D spectra
The visible pulse can be shaped into a collinear four-pulse sequence utilizing a pulse shaper in the beam path, enabling different experimental configurations: coherent 2D spectroscopy using only the visible four-pulse sequence (Fig. 1a), transient 2D spectroscopy combining the UV pulse and the visible probe sequence (Fig. 1b), and conventional pump–probe spectroscopy using a single UV and a single visible pulse (Fig. 1c)
Summary
Coherent two-dimensional (2D) optical spectroscopy has revolutionized our ability to probe many types of couplings and ultrafast dynamics in complex quantum systems. 1234567890():,; Traditionally, molecular-beam spectroscopy is used in a pump–probe implementation with photoelectron or -ion detection for the gas-phase investigation of transition states in photochemistry[1], vibrational wavepackets[2,3,4], or excited-state dynamics of biologically relevant molecules[5,6,7] Ultracold samples such as helium nanodroplets[8] facilitate, for example, the investigation of multiple-quantum coherences[9, 10]. Coherent 2D spectroscopy on molecular beams can serve as a complementary tool to condensed-phase techniques resolving otherwise congested 2D spectra of transitions in complex systems due to the narrow linewidths of a gas-phase sample It further enables the investigation of bound–continuum transitions and corresponding lineshapes by detecting the ionization products
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