Observation of the Infrared Spectrum of the Hydrogen Molecular Ion HD+

High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level

“…Third, the result presented here can be used to obtain a new value the proton-to-electron mass ratio with a precision of 2.9 p.p.b. [12], for the first time from molecular spectroscopy as proposed already four decades ago [5].…”

“…Already four decades ago, Wing et al [5] performed measurements of ro-vibrational transitions in HD + and conjectured that such measurements could be used to test quantum electrodynamics (QED) theory in molecules and lead to an improved value of the proton-to-electron mass ratio, μ. Today, QED corrections to ro-vibrational transition frequencies in H + 2 and HD + have been calculated up to the order m e α 8 , with m e the electron mass and α the fine-structure constant, leading to relative uncertainties of the order of 3-4 × 10 −11 [1,2].…”

IR Spectroscopy of Hydrogen Bonded Charged Clusters

“…Infrared spectra of species such as NH 4 + and HN 2 + have been obtained with very high resolution because of the kinematic compression of the infrared Doppler profile in the fast beam. 41 In order to obtain sufficient ion beam current for direct absorption studies, the technique uses a discharge followed by expansion with a low backing pressure (10 torr is typical) through a large orifice (1 or 2 mm diameter) with several kVjcm extraction voltage to generate ~amps of ion beam current. Under these conditions, the ions can be quite hot vibrationally, since they are accelerated before entering the collisionless regime.…”

Indirect Rotational Spectroscopy of HCO+

“…Since the late 1980s, the predominant tool for this has been velocity modulation spectroscopy (VMS). The groundwork of VMS was laid by Wing et al in a velocity modulated ion beam, 1 and the first application of VMS as it is known today was by Gudeman et al in a velocity modulated positive column discharge cell. 2 Since the initial work, the technique has become a mainstay in ion spectroscopy and has been extensively reviewed.…”