Accessing Excited State Molecular Vibrations by Femtosecond Stimulated Raman Spectroscopy

TL;DR

This paper introduces a method using femtosecond stimulated Raman spectroscopy with controlled pulse timing to distinguish and analyze vibrational modes in both ground and excited electronic states of molecules, exemplified on Cresyl Violet.

Contribution

It presents a novel approach combining pulse timing control and diagrammatic analysis to disentangle ground and excited state vibrations in resonance conditions.

Findings

Successfully disentangled ground and excited state vibrational signals.

Applied method to Cresyl Violet to reveal vibrational properties.

Potential to map reaction coordinates in photo-active compounds.

Abstract

Excited-state vibrations are crucial for determining photophysical and photochemical properties of molecular compounds. Stimulated Raman scattering can coherently stimulate and probe molecular vibrations with optical pulses, but it is generally restricted to ground state properties. Working in resonance conditions, indeed, enables cross-section enhancement and selective excitation to a targeted electronic level, but is hampered by an increased signal complexity due to the presence of overlapping spectral contributions. Here, we show how detailed information on ground and excited state vibrations can be disentangled, by exploiting the relative time delay between Raman and probe pulses to control the excited state population, combined with a diagrammatic formalism to dissect the pathways concurring to the signal generation. The proposed method is then exploited to elucidate the vibrational properties of ground and excited electronic states in the paradigmatic case of Cresyl Violet. We anticipate that the presented approach holds the potential for selective mapping the reaction coordinates pertaining to transient electronic stages implied in photo-active compounds.