Clemens Hofmann | Searcharxiv

arXiv2026

Is There Elliptic Distortion in the Light Harvesting Complex 2 of Purple Bacteria?

Single molecule spectroscopy (SMS) revealed unusually large gap between two major exciton peaks of the B850 unit of light harvesting complex 2 (LH2), which could be explained assuming elliptic distortion or k=2 symmetry modulation in the site excitation energy. On the basis of extensive simulation of the SMS data and ensemble lineshape, we found that uniform modulation of k=2 symmetry cannot explain the dependence of intensity ratios on the gap of the two major peaks, which are available from SMS, nor the ensemble lineshape. Alternative models of disorder with k=1 and k=2 symmetry correlation are shown to reproduce these data reasonably well and can even explain the gap distribution when it is assumed that the lower major peak in the SMS lineshape is an intensity weighted average of k=1- and k=0 states.

physics.bio-ph↗

arXiv2025

Ultra-resolution photochemical sensing

Photochemistry in the earth's atmosphere is driven by the sun, continuously altering the concentration and spatial distribution of pollutants. Precisely monitoring their atmospheric abundance relies predominantly on optical sensing, which requires the knowledge of exact absorption cross sections. One key pollutant which impacts many photochemical reaction-pathways is formaldehyde. Agreement on formaldehyde absolute absorption cross section remains elusive in the photochemically-relevant ultraviolet spectral region, hampering sensitive concentration tracking. Here, we introduce free-running ultraviolet dual comb spectroscopy, combining high spectral resolution (1 GHz), broad spectral coverage (12 THz), and fast acquisition speed (500 ms), as a novel method for absolute absorption cross section determination with unprecedented fidelity. Within this bandwidth, our method uncovers almost one order of magnitude more rovibrational transitions than detected before which leads to refined rotational constants for high-level quantum simulations of molecular eigenstates. This ultra-resolution method can be generalized to provide a universal tool for fast electronic fingerprinting of atmospherically-relevant species, both for sensing applications and to benchmark improvements of ab-initio quantum theory.

physics.optics↗