Abstract
Context. The high spectral resolution R ∼ 45 000 provided by IGRINS (Immersion Grating INfrared Spectrometer) at MacDonald Observatory and R ∼ 100 000 achieved by CRIRES (CRyogenic high-resolution InfraRed Echelle Spectrograph) at VLT (Very Large Telescope) challenges the present knowledge of infrared spectra. Aims. We aim to predict the full infrared spectrum of molecular hydrogen at a comparable accuracy. Methods. We take advantage of the recent theoretical ab initio studies on molecular hydrogen to compute both the electric quadrupole and magnetic dipole transitions taking place within the ground electronic molecular state of hydrogen. Results. We computed the full infrared spectrum of molecular hydrogen at an unprecedented accuracy and derive for the first time the emission probabilities including both electric quadrupole (ΔJ = 0, ±2) and magnetic dipole transitions (ΔJ = 0) as well as the total radiative lifetime of each rovibrational state. Inclusion of magnetic dipole transitions increases the emission probabilities by factors of a few for highly excited rotational levels, which occur in the 3–20 μ range.
Highlights
Molecular hydrogen (H2) is a symmetric molecule, which prohibits electric dipole transitions to occur within its X1Σ+g ground electronic state
Considerable attention has been paid to the ab initio studies of this simple molecule where the resolution of the one dimensional Schrödinger equation allows the energy spectrum of the ground electronic state to be derived, as described in the pioneering work by Kołos & Wolniewicz (1964)
Various corrections have been further introduced in order to compare the theoretical ab initio values to the experimentally derived values by Dabrowski (1984) from the VUV (Vacuum Ultra-Violet) absorption and emission flash discharge spectra of H2 in the Lyman and Werner bands
Summary
Molecular hydrogen (H2) is a symmetric molecule, which prohibits electric dipole transitions to occur within its X1Σ+g ground electronic state. Astrophysical observations in the infrared have allowed the detection of tens of highly H2 excited emission rovibrational transitions occuring in socalled Photon dominated regions (PDRs) such as the Orion Bar (Kaplan et al 2017) or NGC 7023 (Le et al 2017) or in shocked regions such as the Orion KL outflow (Oh et al 2016; Geballe et al 2017) and Herbig-Haro objects (Pike et al 2016). We find that it is timely to provide the complete infrared spectrum of H2 involving any possible transition linking all available rovibrational levels at the highest level of accuracy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
