Densities, infrared band strengths, and optical constants of solid methanol

Abstract

Contact. The increasing capabilities of space missions like the James Webb Space Telescope or ground-based observatories like the European Extremely Large Telescope demand high quality laboratory data of species in astrophysical conditions for the interpretation of their findings. Aims. We provide new physical and spectroscopic data of solid methanol that will help to identify this species in astronomical environments. Methods. Ices were grown by vapour deposition in high vacuum chambers. Densities were measured via a cryogenic quartz crystal microbalance and laser interferometry. Absorbance infrared spectra of methanol ices of different thickness were recorded to obtain optical constants using an iterative minimization procedure. Infrared band strengths were determined from infrared spectra and ice densities. Results. Solid methanol densities measured at eight temperatures vary between 0.64 g cm−3 at 20 K and 0.84 g cm−3 at 130 K. The visible refractive index at 633 nm grows from 1.26 to 1.35 in that temperature range. New infrared optical constants and band strengths are given from 650 to 5000 cm−1 (15.4–2.0 μm) at the same eight temperatures. The study was made on ices directly grown at the indicated temperatures, and amorphous and crystalline phases have been recognized. Our optical constants differ from those previously reported in the literature for an ice grown at 10 K and subsequently warmed. The disagreement is due to different ice morphologies. The new infrared band strengths agree with previous literature data when the correct densities are considered.

Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices

“…In our fixed-energy experiments, we irradiated pure methanol ice with fluences between 5 × 10 15 photon cm −2 and 2 × 10 16 photon cm −2 . Because we irradiated a volume of 0.1 cm 2 × 100 ML, with a mean energy of ∼550 eV, and when we consider a volumic mass of condensed methanol of ∼0.64 g cm −3 (at 20 K; Luna et al 2018) and an X-ray absorption cross section of ∼0.6 Mbarn (Ishii & Hitchcook 1988), the absorbed doses used in our fixed energy experiments change from ∼2 to ∼15 MGy, which is quite similar to the absorbed doses in Laffon et al (2010). This indicates that we could expect a methanol destruction rate of about 50% for our low-fluence experiments.…”

The influence of molecular vicinity (expressed in terms of dielectric constant) on the infrared spectra of embedded species in ices and solid matrices

“…The chemical environments expressed in terms of the different type of neighbor molecules around a given embedded species and its inuence on IR proles were also discussed by Schimitt et al 31 Similarly, the changes in the band strengths with chemical composition were extensively investigated experimentally in the literature. [32][33][34][35] As the surrounded species changes, the electric eld and dielectric constant of the medium change, and this affects the molecular orbital and atom conguration of the embedded species (as well as electric dipole moments) which interact differently with the incoming electromagnetic eld. These changes result, as a consequence, changes in the molecular band strength for a given energy transition (or vibration mode).…”

Infrared complex refractive index of N-containing astrophysical ices free of water processed by cosmic-ray simulated in laboratory

“…As such experimental parameters used in this paper are very sensitive to the chemical composition as shown in Luna et al [19,21], the values of , and 0 , were estimated from the confidence limits (See Appendix). Due to uncertainties involved in the initial parameters, the error for and were around 12%.…”

“…Apart of the chemical interest in N-containing ices, the complex refractive index (henceforth called CRI) is an important parameter, as it determines how the material interacts with electromagnetic radiation. In addition, it records the chemical variation triggered by the ionizing radiation such as UV, X-rays and Cosmic-rays [16,17,18,19,20,21]. On this subject, the aim of this paper is not to provide a detailed description of the chemical synthesis after ion bombardment of the ices, but instead, to provide a new CRI database, calculated from different N-containing ice samples, and contribute to reduce the huge lack of this kind of data in the astronomical community.…”