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Context.The methyl cation (CH3+) has recently been discovered in the interstellar medium through the detection of 7 μm (1400 cm−1) features toward the d203-506 protoplanetary disk by the JWST. Line-by-line spectroscopic assignments of these features, however, were unsuccessful due to complex intramolecular perturbations preventing a determination of the excitation and abundance of the species in that source. Aims.Comprehensive rovibrational assignments guided by theoretical and experimental laboratory techniques provide insight into the excitation mechanisms and chemistry of CH3+in d203-506. Methods.The rovibrational structure of CH3+was studied theoretically by a combination of coupled-cluster electronic structure theory and (quasi-)variational nuclear motion calculations. Two experimental techniques were used to confirm the rovibrational structure of CH3+:(1) infrared leak-out spectroscopy of the methyl cation, and (2) rotationally resolved photoelectron spectroscopy of the methyl radical (CH3). In (1), CH3+ions, produced by the electron impact dissociative ionization of methane, were injected into a 22-pole ion trap where they were probed by the pulses of infrared radiation from the FELIX free electron laser. In (2), neutral CH3, produced by CH3NO2pyrolysis in a molecular beam, was probed by pulsed-field ionization zero-kinetic-energy photoelectron spectroscopy. Results.The quantum chemical calculations performed in this study have enabled a comprehensive spectroscopic assignment of thev2+andv4+bands of CH3+detected by the JWST. The resulting spectroscopic constants and derived EinsteinAcoefficients fully reproduce both the infrared and photoelectron spectra and permit the rotational temperature of CH3+(T= 660 ± 80 K) in d203-506 to be derived. A beam-averaged column density of CH3+in this protoplanetary disk is also estimated.
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Infrared Laser Stark Spectroscopy of Methyl Fluoride in 4 He Nanodroplets
Abstract We measured the rotationally resolved infrared spectra of helium solvated methyl fluoride at 3 μm and 10 μm, wherein lies C−H and C−F stretching bands, respectively. The linewidths (FWHM) were found to increase with increasing vibrational energy and range from 0.002 cm−1in thev3band (C−F stretch) at ~1047 cm−1, to 0.65 cm−1in thev4band (asymmetric C−H stretch) at ~2997 cm−1. In between these two bands we observed the lower and upper components of the Fermi triad bands (ν1/2ν2/2ν5) at ~2859 and ~2961 cm−1. We carried out Stark spectroscopy on the lower band on account of its narrower linewidths (0.04 vs. 0.14 cm−1, respectively). The objective of performing Stark spectroscopy was to see if there is any evidence for a rotational linewidth dependence on the external field strength, due to a reduced difference in between methyl fluorides rotational energy gap and the roton‐gap of superfluid helium. We did not find any evidence for such an effect, which we largely attribute to the rotational energy gap not increasing significantly enough by the external field. We point to another molecule (formaldehyde) whose energy levels are predicted to show a more promising response to application of an external field.
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- Award ID(s):
- 2418212
- PAR ID:
- 10569037
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 25
- Issue:
- 12
- ISSN:
- 1439-4235
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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