Sketching the 75th International Symposium on Molecular Spectroscopy (ISMS) - Day 1
Olivia Wilkins
I was at home from AAS 240 for about 21 hours before I left for the airport, this time to fly to the Midwest. Today was the first day of the 75th International Symposium on Molecular Spectroscopy (ISMS), known affectionately as the “donut conference” for the mountain of donuts stocked in the library of the chemistry building on the University of Illinois at Urbana-Champaign (UIUC) campus.
Once again, I’ve brought my sketchbook and colored pencils to sketch summaries of the talks I attend. Here’s the illustrated summaries from Day 1! (You can also find them on Twitter via #SciConSketch.)
Plenary (Session MA)
Theoretical Descriptions of the Fundamentals of CH, NH, and OH Stretch Vibrations with Simple Models that Include Anharmonic Effects — Edwin Sibert (University of Madison)
The first talk of the day consisted of six vibrational vignettes: energy flow (which talked about the use of statistical energy diagrams); the formic acid (HCOOH) monomer (comparing the perturbations of its two conformational states); peptide conformation preference (determined by high-resolution spectroscopy of large biomolecules); identifying alkylbenzene via UV, IR, and Raman spectroscopy; the interconversion of equatorial and axial orientations of CH in ring molecules via pseudo-rotation; and NH stretch vanishing acts (which asked how hydrogen bonding affects the N-H stretch in large molecules).
Chemistry in the Ultracold Regime: Precision Molecular Assembly and Test of Statistical Reaction Dynamics — Kang-Kuen Ni (Harvard University)
The second plenary started with a brief overview of quantum before talking about how ultracold molecules can be used as “quantum bits,” or qubits in which rotational modes and accompanying hyperfine states of a molecule constitute different qubits. The talk provided an overview of the technique used to form one molecule at a time. Such a feat is possible via laser cooling, and laser light of different wavelengths enable trapping of individual atoms by “optical tweezers.” Surprisingly, using “optical tweezers” isn’t the hardest part of the work discussed. Rather, binding the selected atoms is! Forming bonds is a two-step process: 1. weakly bond the atoms, and 2. shrink the distance between the atoms to form a stronger bond.
Vibrational Spectral Signatures and Dynamics of Strong Intramolecular H-Bonds Investigated with Gas-Phase Ion and Solution-Phase Ultrafast Infrared Spectroscopies — Joseph Fournier (Washington University at St. Louis)
The third plenary talk discussed how gas-phase ion and ultrafast solution-phase infrared (IR) spectroscopies can be highly complementary. Specifically, it talked about a combination of three techniques, namely cryogenic ion vibrational spectroscopy (CIVS), solution-phase transient absorption and 2D IR, and time-resolved CIVS.
New Frontiers in Cosmic Carbon Chemistry — Brett McGuire (MIT)
The fourth plenary was about astrochemistry. It started off by talking about how 80% of compounds in the CAS database (CAS is a division of the American Chemical Society) contain 5- or 6-membered rings, but not many ringed species have been found in space. The question, then, is where are such ringed species in space? The first ring (benzene) was discovered in 2001. It wasn’t until 2018 that the next one was discovered; since 2018, 9 more ringed molecules have been found. Despite not knowing what ringed structures are out there, we know that there is a lot of aromatic carbon (thanks to the diffuse interstellar bands, represented by the lumpy red spectrum in the center of the sketch), but the IR features of such molecules overlap, making it difficult (impossible?) to identify them in the IR. BUT rotational spectra can be resolved and are unique for different cyclic compounds. Using the GBT, benzonitrile was detected in TMC-1 (TMC = Taurus Molecular Cloud), and it was also found (again with the GBT), in several molecular cores in Serpens. Studying such complex species requires lab work and theory (including machine learning).
After Brett’s talk, I needed to give my brain a break (and my phone a charge), so I grabbed some pizza, headed back to my hotel room, picked up a couple of postcards (one for Alex and Gueni, one for a friend I unsuccessfully tried to convince to come to the conference), and stopped by a postbox before heading to my afternoon session.
Astronomy (Session MN)
NOEMA Observations of Complex Organic Chemistry in the W3 Star-Forming Region — Will Thompson (University of Wisconsin-Madison)
W3 is a star-forming region with two cores: W3(H2O) and W3(OH). NOEMA, a radio interferometer in the French Alps and operated by IRAM (French institute for radio astronomy), was used to compare the spectra of the two cores. While the chemistry of both cores was comparable for most molecules, there were a few things distinct about W3(H2O) and W3(OH). For instance, ethyl cyanide (CH3CH2CN) was found in only one of the cores (W3(H2O)), while H II emission (i.e., H+) was detected in the other (W3(OH)). The presence of an H II region in W3(OH) suggests that this core is more evolved than its counterpart, which may explain the differences in chemical composition.
Using HCO+ Line (& Its Isomers) As An Astrochemical Probe of the Structure of Class 0/I Protostars — Mihika Rao (University of Virginia)
Some circumstellar disks around Class 0/I (i.e., very young) protostars already have gaps and rings, which may indicate that planet formation begins well before the protoplanetary stage. The presented work looked at a sample of such objects, including BHR 71, to study HCO+, HOC+, H13CO+, DCO+, and HC18O+. A curious first finding is that the HCO+ emission in BHR 71 is perpendicular to the continuum, which is dominated by dust emission. The HCO+/DCO+ and HCO+/HC18O+ ratios measured were what was expected based on previous observations; however, the ratio between HCO+ and H13CO+ was much lower than predicted. The reason for this is unknown but will be investigated moving forward.
Magnetic Field Strength Limits in a Protoplanetary Disk from Multi-Wavelength Zeeman Observations — Rachel Harrison (UIUC)
In this talk, spectroscopy was used to look at something other than chemistry, which was really interesting to hear about from the perspective of an astrochemist. An open question about protoplanetary disks is, "How do you transport enough material inward to be accreted onto the central star of a disk [so that it can begin to fuse hydrogen]?" One idea is that magnetohydrodynamics remove mass from the disk to conserve angular momentum, which is possible because of polarized radiation aligning dust grains with respect to a magnetic field. This was studied by considering Zeeman splitting, in which a spectral line is split into multiple components when a magnetic field is applied. Observations of CN were used to place an upper limit on magnetic field strengths in disks.
Detection of c-C3H2, NO, and CH3CN towards Molecular Clouds at the Edge of the Galaxy — Lilia Kaelemay (University of Arizona)
This talk introduced the concept of the Galactic Habitable Zone. A common astrobiological consideration are the habitable zones around stars, which are typically defined as the distances from a star where a planet could host liquid water on its surface. The Galactic Habitable Zone (GHZ) are the portions of the Milky Way where chemistry could give rise to organic life. There have been several GHZs proposed previously, including at 7-9 kpc from the galactic center (which is where the solar system resides, at 8 kpc from the galactic center). Other GHZs proposed include 0-2 kpc and at radii up to 16 kpc. Using the ARO (Arizona Radio Observatory) 12-meter telescope at Kitt Peak (shown by the bottom left sketch), small (<50 pc) clouds at distances of more than 10 kpc from the galactic center were observed. Several species were detected, including c-C3H2, NO, and CH3CN. Some of the regions where these compounds were found were near the edge of the galaxy, suggesting that the GHZ boundaries could be pushed to 25 kpc from the galactic center.
Molecules in the Early Universe (Z=6.9) — Sreevani Jarugula (UIUC)
Galaxies at redshifts of Z=6.9 are those that exist 800 million years after the Big Bang, so observing them is looking about 13 billion years back in time! These galaxies reside just after what is called the epoch of reionization, when the first stars and first light emerged. The galaxies studied were SPT 0311-58. Because they are so far away, they were observed using a technique called gravitational lensing in which their observed radio waves are bended around a foreground star. Both CO and H2O were detected, and models suggest the chemistry is similar to nearby galaxies with active nuclei (i.e., AGNs, or active galactic nuclei).
High-Resolution Mid-IR Observations of SiO and the Search for TiO in the Circumstellar Envelope of the Variable Star χ Cyg — Guido Fuchs (Universität Kassel)
Late in their lives, stars eject material into space. This material includes silicon monoxide (SiO), titanium oxide (TiO), and vanadium oxide (VO). For TiO to be detected around an old star, however, TiO first needed to be measured in the lab. Once that was complete, the Infrared Telescope Facility (IRTF) was used to observe χ Cygnus, a variable star with a 408-day period. χ cyg goes between being small and hot, when it also ejects a lot of material, and larger and cooler. This means that SiO emission is variable too, a fact that can be used to tease out weak signals in noisy spectra. A search for TiO is in progress, and TiO seems to have been found!
Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 — Mark Siebert (University of Virginia)
IRC+10216 (also known as CW Leonis) is a carbon star with a dusty extended envelope. It is located at a distance of 130 pc from the solar system, and it is the site where 55 out of nearly 270 molecules were first detected in space. Observations of HC3N revealed asymmetric carcs and clumps, some extended emission, and a strong clump to the southwest (the SW clump). An overabundance of HC3N would require photochemistry to break apart HCN, which could then react with C2H2 to form HC3N. However, the HC3N profile was found to match that of CO, so it is not the result of varying chemistry across the envelope but just the asymmetric density. However, this could be the result of a stellar companion (making IRC+10216 part of a binary system) that is deeply embedded in the envelope. Although it can't be seen, models of a second star with a temperature of 6000 Kelvin account for the strange morphology of the system.
ALMA Reveals the Molecular Outflows in the Envelope of Hypergiant VY Canis Majoris — Ambesh Singh (University of Arizona)
VY Canis Majoris has an envelope characterized by three dusty arcs. Spectroscopy of CO, SO2, and OH reveal outflows that have multiple velocity components. ALMA observations revealing the spatial distributions of these compounds show that they clearly trace asymmetric ejecta from VY Canis Majoris.
Re-examine the Chemistry in Protoplanetary Nebulae: M1-92, Cotton Candy Nebula, and IRAS 22036 — Kate Gold (University of Arizona)
Observations of AGB stars (late-stage stars) and planetary nebulae (nebulae around very old stars) reveal distinct profiles for the abundances of different compounds with respect to molecular hydrogen, or H2 with age. However, what happens in between these two stages—at the protoplanetary nebula stage—has not yet been explored. To explore the relative abundances of different compounds, three protoplanetary nebulae—M1-92, the Cotton Candy Nebula, and IRAS 22036—were observed. There were several interesting findings, one of which is the presence of H2S and its isotopologues, H233S and H234S. The abundances of these isotopologues are enhanced well above what is expected from the relative solar abundances. These sources are full of isotopic enhancements that will be explored in the future.
An Absorption Survey of C3H+ and C4H in Diffuse Clouds toward Galactic Continuum Regions — Harshal Gupta (National Science Foundation)
Only about one-fifth of interstellar molecules have been detected in diffuse clouds. These include 14 ions and 22 radicals. Two compounds known to reside in diffuse interstellar media are C3H+ and C4H (the largest carbon-chain radical definitively known). The compound C3H+ was first detected in the Horsehead Nebula, and C4H was first detected in IRC+10216. Observations were carried out using the Green Bank Telescope (GBT) toward a number of regions to survey the prevalence of these two molecules. This work is ongoing and could help us understand the peculiarities of carbon-chain chemistry in diffuse media.