Context. Infrared spectroscopy of star and planet forming regions is at the dawn of a new age with the upcoming James Webb Space Telescope (JWST). Its high resolution and unprecedented sensitivity... Show moreContext. Infrared spectroscopy of star and planet forming regions is at the dawn of a new age with the upcoming James Webb Space Telescope (JWST). Its high resolution and unprecedented sensitivity allows us to probe the chemical complexity of planet forming regions, such as dense clouds, embedded protostars, and protoplanetary disks, both in the solid state and gas phase. In support of these observations, laboratory spectra are required to identify complex organic molecules in the ices that cover the dust grains in these regions.Aims. This study aims to provide the necessary reference spectra to firmly detect methyl formate (HCOOCH3) in the different evolutionary stages of star and planet forming regions. Methyl formate is mixed in astronomically relevant matrices, and the peak positions, full width at half maximum, and relative band intensities are characterized for different temperatures to provide an analytical tool for astronomers.Methods. Methyl formate was deposited at 15 Kelvin on a cryogenically cooled infrared transmissive window under high-vacuum conditions. Specifically, methyl formate was deposited pure and mixed with CO, H2CO, CH3OH, H2O, and CO:H2CO:CH3OH combined. The sample was linearly heated until all solid-state constituents were desorbed. Throughout the experiment, infrared spectra were acquired with a Fourier transform infrared spectrometer in the range from 4000 to 500 cm(-1) (2.5-20 mu m) at a spectral resolution of 0.5 cm(-1).Results. We present the characterization of five solid-state methyl formate vibrational modes in pure and astronomically relevant ice matrices. The five selected vibrational modes, namely the C=O stretch (5.804 mu m), the C-O stretch (8.256 mu m), CH3 rocking (8.582 mu m), O-CH3 stretching (10.98 mu m), and OCO deformation (13.02 mu m), are best suited for a JWST identification of methyl formate. For each of these vibrational modes, and each of the mixtures the temperature versus spectra heatmaps, peak position versus full width at half maximum and relative band intensities are given. All spectra are publicly available on the Leiden Ice Database. Additionally, the acquired reference spectra of methyl formate are compared with archival Spitzer observations of HH 46. A tentative detection of methyl formate provides an upper limit to the column density of 1.7 x 10(17) cm(-2), corresponding to an upper limit relative to water of <= 2.2% and <= 40% with respect to methanol. Show less
A number of recent experimental studies have shown that solid-state complex organic molecules (COMs) can form under conditions that are relevant to the CO freeze-out stage in dense clouds. In this... Show moreA number of recent experimental studies have shown that solid-state complex organic molecules (COMs) can form under conditions that are relevant to the CO freeze-out stage in dense clouds. In this work, we show that alcohols can be formed well before the CO freeze-out stage (i.e., during the very early stage of the H2O-rich ice phase). This joint experimental and computational investigation shows that isomers n-propanol and isopropanol (H3CCH2CH2OH and H3CCHOHCH3) and n-propenol and isopropenol (H3CCH=CHOH and H3CCOH=CH2) can be formed in radical-addition reactions starting from propyne (H3CC CH) + OH at the low temperature of 10 K, where H3CC CH is one of the simplest representatives of stable carbon chains already identified in the interstellar medium (ISM). The resulting average abundance ratio of 1:1 for n-propanol:isopropanol is aligned with the conclusions from the computational work that the geometric orientation of strongly interacting species is influential to the extent of which "mechanism" is participating and that an assortment of geometries leads to an averaged-out effect. Three isomers of propanediol are also tentatively identified in the experiments. It is also shown that propene and propane (H3CCH=CH2 and H3CCH2CH3) are formed from the hydrogenation of H3CC CH. This experimental finding falls in line with the lower activation barrier of hydrogenation of a C=C bond in comparison to a C C bond. Reactants and products are probed by temperature-programmed desorption-quadrupole mass spectrometry (TPD-QMS) and reflection absorption infrared spectroscopy (RAIRS). Product relative abundances are determined from TPD-QMS data. Computationally derived activation barriers give additional insight into what types of reactions and mechanisms are more likely to occur in the laboratory and in the ISM. Our findings not only suggest that the alcohols studied here share common chemical pathways and therefore can show up simultaneously in astronomical surveys but also that their extended counterparts that derive from polyynes containing H3C-(C C)(n)-H structures may exist in the ISM. Such larger species, such as fatty alcohols, are the possible constituents of simple lipids that primitive cell membranes on the early Earth are thought to be partially composed of. Show less
