Processing of formic acid-containing ice by heavy and energetic cosmic ray analogues

TL;DR

This study examines how heavy cosmic ray analogues interact with formic acid-containing ice, revealing molecular dissociation and formation of new species, which has implications for astrochemical processes and pre-biotic molecule formation.

Contribution

It provides experimental data on the effects of heavy cosmic rays on formic acid ice, including dissociation cross-sections and molecular transformations relevant to space environments.

Findings

Dissociation cross-section for formic acid: 2.4x10^-13 cm^2

Half-life due to galactic cosmic rays: 8x10^7 years

Formation of CO and CO2 observed in IR spectra

Abstract

Formic acid (HCOOH) has been extensively detected in space environments, including interstellar medium (gas and grains), comets and meteorites. Such environments are often subjected to the action of ionizing agents, which may cause changes in the molecular structure, thus leading to formation of new species. Formic acid is a possible precursor of pre-biotic species, such as Glycine (NH2CH2COOH). This work investigates experimentally the physicochemical effects resulting from interaction of heavy and energetic cosmic ray analogues (46MeV 58Ni11+) in H2O:HCOOH (1:1) ice, at 15 K, in ultrahigh vacuum regime, using Fourier transform infrared spectrometry in the mid-infrared region (4000-600 cm-1 or 2.5-12.5 microns). After the bombardment, the sample was slowly heated to room temperature. The results show the dissociation cross-section for the formic acid of 2.4x10^-13 cm2, and half-life due to galactic cosmic rays of 8x10^7 yr. The IR spectra show intense formation of CO and CO2, and small production of more complex species at high fluences.