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Updated: Mar 9, 2026
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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
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Trans-cis molecular photoswitching in interstellar Space
S Cuadrado1, J R Goicoechea1, O Roncero2
1Grupo de Astrofísica Molecular. Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Sor Juana Ines de la Cruz 3, E-28049 Cantoblanco, Madrid, Spain.
Astronomy and Astrophysics
|December 23, 2016
Summary
Astronomers detected cis-formic acid (cis-HCOOH) in space for the first time, challenging previous assumptions about its interstellar abundance. This discovery suggests ultraviolet radiation can alter molecular structures in space.
Area of Science:
- Astrochemistry
- Molecular Physics
- Interstellar Medium
Background:
- Organic molecules like formic acid (HCOOH) exist in two spatial arrangements called conformers: trans and cis.
- The trans conformer of formic acid is more stable and was previously thought to be the only one present in detectable amounts in interstellar clouds due to a high energy barrier for conversion.
- Interstellar environments are rich in ultraviolet (UV) radiation, which can influence molecular chemistry.
Purpose of the Study:
- To report the first detection of the cis conformer of formic acid (cis-HCOOH) in interstellar space.
- To investigate the mechanism responsible for the presence of cis-HCOOH in UV-irradiated regions.
- To explore the potential role of UV radiation in inducing structural changes in interstellar molecules.
Main Methods:
- Astronomical observation of the Orion Bar photodissociation region.
- Ab initio quantum calculations to study molecular behavior under UV radiation.
- Analysis of molecular abundance ratios, specifically the trans-to-cis ratio of formic acid.
Main Results:
- The first definitive detection of cis-HCOOH in an interstellar environment.
- cis-HCOOH was found exclusively in UV-irradiated gas, specifically within the Orion Bar.
- A low trans-to-cis abundance ratio (2.8 ± 1.0) was measured, indicating significant cis-HCOOH presence.
Conclusions:
- The detection of cis-HCOOH supports a photoswitching mechanism, where UV photons alter molecular conformers.
- This photoswitching mechanism, involving excitation and subsequent decay, likely drives the formation of cis-HCOOH.
- The findings suggest that UV radiation may induce conformational changes in various interstellar molecules, a process previously unconsidered.
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