# Structure determination of the tetracene dimer in helium nanodroplets using femtosecond strong-field ionization

## TL;DR

This study uses femtosecond strong-field ionization and covariance analysis to determine the structure of tetracene dimers in helium nanodroplets, identifying their conformations and potential for singlet fission.

## Contribution

It introduces a novel method combining covariance analysis and laser alignment to determine dimer conformations in helium nanodroplets.

## Key findings

- Identified tetracene dimer conformations consistent with experimental covariance maps.
- Narrowed down possible structures to slipped-parallel or parallel-slightly-rotated conformations.
- Found one conformation favorable for singlet fission, relevant for organic electronics.

## Abstract

Dimers of tetracene molecules are formed inside helium nanodroplets and identified through covariance analysis of the emission directions of kinetic tetracene cations stemming from femtosecond laser-induced Coulomb explosion. Next, the dimers are aligned in either one or three dimensions under field-free conditions by a nonresonant, moderately intense laser pulse. The experimental angular covariance maps of the tetracene ions are compared to calculated covariance maps for seven different dimer conformations and found to be consistent with four of these. Additional measurements of the alignment-dependent strong-field ionization yield of the dimer narrows the possible conformations down to either a slipped-parallel or parallel-slightly-rotated structure. According to our quantum chemistry calculations, these are the two most stable gas-phase conformations of the dimer and one of them is favorable for singlet fission.