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  • Astronomical CH3+ rovibrational assignments: A combined theoretical and experimental study validating observational findings in the d203-506 UV-irradiated protoplanetary disk
Title: Astronomical CH3+ rovibrational assignments: A combined theoretical and experimental study validating observational findings in the d203-506 UV-irradiated protoplanetary disk
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.  more » « less
Award ID(s):
2110489
PAR ID:
10528747
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more » ; ; ; ; ; ; ; ; « less
Publisher / Repository:
EDP Sciences
Date Published:
Journal Name:
Astronomy & Astrophysics
Volume:
680
ISSN:
0004-6361
Page Range / eLocation ID:
A19
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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