Ices, Ice Irradiation, and Organics Laboratory for Astrobiology (I³OLAB)

Complementary information can be found at the NASA Ames Laboratory Astrophysics I³OLAB pages.

Cryovacuum Sample Systems

Our laboratory contains three different cryovacuum systems (Figure 1) that are used for: (i) preparing ices for spectral measurements, (ii) preparing and irradiating ices to study ice irradiation chemistry, and (iii) producing complex organic residues of astrophysical, astrochemical, and astrobiological interest via ice irradiation chemistry for later analytical study. These systems typically produce vacuums in the 2x10^-8 torr range and are equipped with closed-cycle He cryocoolers that can cool sample fingers in the systems’ sample chambers to temperatures as low as 6–20 K (depending on the system). Two of these systems have the cryocooler mounted horizontally and are used primarily of making ice irradiation residues, while the third has the cryocooler mounted vertically so its sample chamber can be located in the sample chamber of a dedicated desktop infrared (IR) spectrometer (see next section).

Figure 1: Picture of one of our cryovacuum systems. These systems can produce ices at temperatures as low as 6 K and can be equipped with both UV lamp and electron gun radiation sources.

Ice samples are typically made via the condensation of pre-mixed gases (see glass line section below) onto an aluminum foil substrate placed on a cryo-cooled Raman head or a cryo-cooled infrared (IR) transparent window (depending on the system) that is suspended in the middle of the system’s sample chamber. During the deposition, the forming ices can be simultaneously irradiated with UV photons from a microwave-powered H₂ lamp or bombarded by 1.2-keV electrons from an electron gun. The UV lamps emit primarily Lyman-α photons (121.6 nm) in addition to a continuum centered at 160 nm, with an approximate total flux of ~10¹⁵ photons cm^-2 s^-1. Typical irradiation experiments with the UV lamps can last for ~48 hr, which provide a total photon dose that is equivalent to about ~10⁵ years in the diffuse interstellar medium (ISM) or more than 10⁸ years in the dense ISM.

Desktop FTIR Spectrometer

One of our cryovacuum systems has been configured so that an infrared (IR)-transparent cryo-cooled window sits in the sample compartment of a Bio-Rad Excalibur FTS 3000 Fourier-transform infrared (FTIR) spectrometer (Figure 2). The window is positioned so that the IR beam passes though the sample window and exterior windows of the vacuum chamber without obstruction, allowing for real-time collection of transmission spectra during ice deposition, irradiation, and thermal cycling. The substrate can be freely rotated within the vacuum sample chamber to accommodate gas deposition, irradiation by energetic source (UV lamp or electron gun), or IR spectral measurements. The spectrometer can measure spectra in both the near-IR (NIR) and mid-IR (MIR) ranges using a selection of beamsplitters and IR detectors. MIR spectra are collected in the 6000–600 cm⁻¹ spectral range at a resolution of 1 cm⁻¹ using a liquid nitrogen-cooled mercury–cadmium–telluride (MCT) detector and a KBr beamsplitter, while NIR spectra are collected in the 10000–4000 cm⁻¹ range using the same detector and a quartz beamsplitter. The signal to noise of the final spectra is established by selecting the number of scans to be taken and co-added, and calibrated spectra are obtained by ratioing the single beam spectrum of the sample and sample window with a single beam spectrum of the window by itself.

Figure 2: Our cryovacuum system integrated with a Bio-Rad Excalibur FTS 3000 Fourier-transform infrared (FTIR) spectrometer.

IR Microscopy Capability

Our Nicolet iN10 MX Fourier-transform infrared (FTIR) microscope is a stand-alone device (Figure 3) used to analyze a wide variety of samples, including organic residues produced from the UV irradiation of astrophysical ice analogs, residues themselves irradiated with high-energy photons, and meteoritic samples. The IR microscope provides information about the chemical compositions of these samples down to a spatial resolution of 5 μm and a spectral resolution down to 1 cm^-1 by collecting transmission or reflection spectra in the mid-IR (4000‒650 cm^-1; 2.5‒15.4 μm) and near-IR (7000‒4000 cm^-1; 1.42‒2.5 μm) ranges, thanks to an LN₂-cooled MCT detector and a KBr beamsplitter. The OMNIC Picta software used to run the IR microscope is equipped with a built-in OMNIC spectral library to help with the interpretation of the collected spectra.

Figure 3: Picture of the IR microscope used in our laboratory for the analysis a variety of samples that include laboratory residues produced from the UV irradiation of astrophysical ice analogs and meteoritic samples.

An example of the use of the IR microscope is for the analysis of several stones from the Sutter’s Mill meteorite (Figure 4). These IR spectra showed a number of absorption features associated with the presence of minerals, including phyllosilicates, olivines, pyroxenes, carbonates, as well as organics.

Figure 4: Infrared spectrum (4000–650 cm^-1) of the fragment of a stone from the Sutter’s Mill meteorite showing the presence of carbonates (C), phyllosilicates (PS), and a combination of bands associated with aliphatic hydrocarbons (A) and overtones of carbonates (C).

Gas Chromatography coupled to Mass Spectrometry (GC-MS) Capability

Our gas chromatography coupled to mass spectrometry (GC-MS) device combines a Thermo Trace gas chromatograph with a Thermo DSQ II mass spectrometer (Figure 5), which can record mass spectra in the 50–650 Da mass range. Using a variety of GC columns (Rxi-5ms, Rtx-200MS, DB-17HT, etc.), derivatization techniques (BSTFA, MTBSTFA, etc.), and temperature gradients, this GC-MS instrument can separate the organic components of a wide variety of complex mixtures from samples produced in the laboratory or extraterrestrial materials. The identification of compounds in samples is made by comparison of the retention times and mass spectra of their GC peaks with commercial standards prepared and derivatized in the same manner as the samples. In the absence of relevant standards, mass fragmentation spectra can provide constraints on the family of molecules to which unidentified compounds belong. In addition, the built-in NIST database provided with the GC-MS analysis software (Xcalibur) can help with the identification of compounds for which standards are not available.

Figure 5: Picture of the GC-MS device used in the I3OLAB.

For example, GC-MS analysis of organic residues produced from the UV irradiation of simple ice mixtures consisting of H₂O and CH₃OH resulted in the identification of the ribose and 2-deoxyribose, i.e., the sugars that constitute the molecular backbones of RNA and DNA, respectively (Figure 6).

Figure 6: Identification of ribose and 2-deoxyribose, the sugars of RNA and DNA, respectively, in the GC-MS chromatogram of an organic residue produced from the UV irradiation of a simple H₂O:CH₃OH ice mixture.

High-Performance Liquid Chromatography (HPLC) Capability

Separation of complex organic mixtures can also be performed using our Agilent Technologies 1100 series high-performance liquid chromatography (HPLC) device (Figure 7). This instrument consists of a quaternary pump with a diode array UV detector and four-channel fluorescence detector. Separation of samples are performed using a combination of LC columns, solvents, and solvent gradients. Typical HPLC columns include Supelco Discovery^® C18 (size: 250 × 4.6 mm, inner diameter: 5 μm) and Phenomenex Luna 5μm Phenyl-Hexyl (size: 250 × 4.60 mm, inner diameter: 5 μm) columns. Solvents used include water, methanol, acetonitrile, pH buffers, etc.

Figure 7: Picture of the HPLC used in our laboratory.

HPLC separation of a laboratory residue produced from the UV irradiation of astrophysical ice analogs of composition H₂O:CH₃OH:CO:NH₃ that led to the identification of the amino acids serine, glycine, and alanine (Figure 8).

Figure 8: HPLC separation of a laboratory residue produced from the UV photolysis of an H₂O:CH₃OH:CO:NH₃ ice mixture and showing the presence of the amino acids serine, glycine, and alanine.

Fluorescence Microscopy Capability

Our laboratory also has an Olympus CKX53 fluorescence microscope equipped with an 89 North PhotoFluor LM-75 light source (Figure 9). Fluorescence microscopy can be used for a variety of applications. One of these applications is the study of amphiphilic compounds that are present in residues produced from the UV irradiation of astrophysical ice analogs and that spontaneously self-assemble into vesicle-like structures (Figure 10). It is yet not clear what fluorescent molecules are present in the membranes of these vesicles.

Figure 9: Picture of the fluorescence microscope.

Figure 10: Vesicles forming spontaneously when organic residues are placed in water and the amphiphiles present in the residues self-assemble into these structures.

Glass line for handing gas samples

Our experiments involving extraterrestrial ice analogs and ice irradiation chemistry require that we be able to prepare a wide variety of gas mixtures for condensation and irradiation. The exact composition of the ices to be made in any given experiment depends on the environment being simulated (interstellar cloud, protostellar disk, comet, icy satellites, etc.) and the scientific question(s) being addressed. Many of our ices can be made from mixtures of relatively simple molecules like H₂O, CH₃OH, CO, CO₂, NH₃, CH₄, N₂, etc., and these mixtures are all prepared on our dedicated glass line (Figure 11), which has a background pressure ~5x10^-6 mbar.

Using glass bulbs of known volumes, complex gas mixtures can be made by mixing individual gas components transferred from dedicated lecture bottles (for example, N₂, CO, NH₃, and CO₂) or evaporated from sample fingers containing volatile liquids (for example, H₂O and CH₃OH). The composition of each mixture is established by measuring the partial pressures of the individual mixed gases (accurate to ~0.05 mbar). The resulting mixtures are stored in 1- to 3-liter glass bulbs that can then be carried to and interfaced with whichever cryovacuum system will be used to make and study the resulting ice.

Figure 11: Picture of the glass line.

References