On the origin of infrared bands attributed to tryptophan in Spitzer observations of IC 348

TL;DR

This study reevaluates the claim that specific infrared features in IC 348 are due to tryptophan, using new JWST data, laboratory spectra, and analysis of instrumental artifacts, ultimately refuting the original assignment.

Contribution

The paper provides a comprehensive reassessment of the tryptophan attribution in interstellar infrared features, incorporating new observational and laboratory data to challenge prior claims.

Findings

JWST data do not support the presence of tryptophan.

Many spectral lines attributed to tryptophan are likely instrumental artifacts.

No compelling evidence for tryptophan in IC 348 from current data.

Abstract

Infrared emission features toward interstellar gas of the IC 348 star cluster in Perseus have been recently proposed to originate from the amino acid tryptophan. The assignment was based on laboratory infrared spectra of tryptophan pressed into pellets, a method which is known to cause large frequency shifts compared to the gas phase. We assess the validity of the assignment based on the original Spitzer data as well as new data from JWST. In addition, we report new spectra of tryptophan condensed in para-hydrogen matrices to compare with the observed spectra. The JWST MIRI data do not show evidence for tryptophan, despite deeper integration toward IC 348. In addition, we show that several of the lines attributed to tryptophan are likely due to instrumental artifacts. This, combined with the new laboratory data, allows us to conclude that there is no compelling evidence for the tryptophan assignment.