Weakly Bound Clusters in Astrochemistry? Millimeter and Submillimeter Spectroscopy of trans-HO₃ and Comparison to Astronomical Observations

Abstract

The emergence of chemical complexity during star and planet formation is largely guided by the chemistry of unstable molecules that are reaction intermediates in terrestrial chemistry. Our knowledge of these intermediates is limited by both the lack of laboratory studies and the difficulty in their astronomical detection. In this work, we focus on the weakly bound cluster HO3 as an example of the connection between laboratory spectroscopic study and astronomical observations. Here, we present a fast-sweep spectroscopic technique in the millimeter and submillimeter range to facilitate the laboratory search for trans-HO3 and DO3 transitions in a discharge supersonic jet and report their rotational spectra from 70 to 450 GHz. These new measurements enable full determination of the molecular constants of HO3 and DO3. We also present a preliminary search for trans-HO3 in 32 star-forming regions using this new spectroscopic information. HO3 is not detected, and column density upper limits are reported. This work provides additional benchmark information for computational studies of this intriguing radical, as well as a reliable set of molecular constants for extrapolation of the transition frequencies of HO3 for future astronomical observations.

Far-Infrared Synchrotron Spectroscopy and Torsional Analysis of the Important Interstellar Molecule, Vinyl Alcohol

“…It is interesting to note that complete vibrational averaging of the dipole moment components (over the 15 vibrational modes) has a similar effect to just torsional averaging them (over ν 15 ), indicating that motion along the CC–O–H dihedral coordinate has by far the greatest effect on the dipole moment components (see Table ). Vibrational averaging of the dipole moment is also known to be important in the related molecules, HCOOH, which has been detected in the ISM, , and HOOO, which has been searched for in the ISM …”

Laser-Induced Chemistry Observed during 248 nm Vacuum Ultraviolet Photolysis of an O3 and CH3NH2 Mixture

“…The molecular absorption signals presented here were obtained using the fast sweep scanning method pioneered by Hays and then optimized by Zou. 9 In brief, the microwave beam is superimposed on a triangle modulation output of the microwave synthesizer. The triangle wave was set to a rate of 10 kHz resulting in five sweeps over a 250 μs window, where the first sweep passed over the 60 μs molecular signal present following the laser pulse, and the fifth sweep was used for background subtraction.…”

“…The molecular absorption signals presented here were obtained using the fast sweep scanning method pioneered by Hays and then optimized by Zou . In brief, the microwave beam is superimposed on a triangle modulation output of the microwave synthesizer.…”

AC Stark Effect Observed in a Microwave–Millimeter/Submillimeter Wave Double-Resonance Experiment

“…The second method involved holding the microwave light on the resonant frequency while the millimeter/submillimeter light was scanned across a 24 MHz wide window using the fast-sweep method developed previously. 64 This fast-sweep method was adapted from a fast-scan submillimeter spectroscopic technique (FASSST) that was developed by the De Lucia group. 65 This technique was later applied to a pulsed supersonic jet to study van der Waals complexes.…”

“…65 This technique was later applied to a pulsed supersonic jet to study van der Waals complexes. 66 For a thorough review on the development of the sweep technique being utilized currently, see Zou et al 64 Spectra were collected at various levels of microwave attenuation (0, 3, 6, 10, 13, 16, and 20 dB). The recorded spectra from this second approach were taken in the frequency domain.…”