Abstract
The predissociation profiles of the R(0), R(1) and R(2) lines of the 3pπ1Πu+,v = 3 ←X1Σg+,v′′ = 0 absorption transition in H2 are calculated in a multichannel quantum defect theory approach, implemented on the basis of state-of-the-art potential energy curves (PEC) from the Wolniewicz group. It is shown that the profiles may be very accurately represented by the Fano profile formula although the resonance parameters thus determined do not exactly coincide with the meaning given to them in Fano's original derivation. The recent high-resolution spectrum of the same transitions taken with the SOLEIL synchrotron is well reproduced by the calculations.
Highlights
IntroductionInspection of the multichannel quantum defect theory (MQDT) wavefunctions of these extra levels indicates that they are discretized vibrational continuum quasi-levels of the 2p C and 3p B states (represented in the figure by blue and red lines, respectively), whose dissociation asymptote lies at 118375.6 cm−1 [H(1 s) + H(n = 2) threshold]
It has been known for a long time that the levels v ≥ 3 of the 3p D 1+ u state of diatomic hydrogenH2 are strongly predissociated by the vibrational continuum of the 3pB which correlates with the H(1 s) + H(n = 2) atomic states [1]
The interaction between the bound and the continuum states leads to broadening of the bound states which have the character of resonances and appear with characteristic line profiles in the photoabsorption spectrum of ground state H2
Summary
Inspection of the MQDT wavefunctions of these extra levels indicates that they are discretized vibrational continuum quasi-levels of the 2p C and 3p B states (represented in the figure by blue and red lines, respectively), whose dissociation asymptote lies at 118375.6 cm−1 [H(1 s) + H(n = 2) threshold]. The saw-tooth pattern of Fig. 1 arises because each quasi-level interacts with 3p , v = 3, N = 1 as its energy is tuned through the bound-level position This interaction leads to an avoided crossing, as shown in the inset of Fig. 2, whose nearest approach 2V is a measure for the discrete ∼ continuum coupling and for the predissociation width. It is evaluated by use of the phase-amplitude Milne approach as implemented in Ref. We do not discuss these aspects in detail here, but refer the reader to the references given
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