Observation of the partial decay intoH0(n’=2) by excitedH−

Abstract

Two resonances in the photodetachment spectrum of H, one just below the n = 3 threshold and the other just below the n =4 threshold, were observed decaying into H {n'=2)+e. The n =3 resonance shows a preference for the n'=2 channel when compared with total-detachment measurements. Fanoline-shape fits give central energies of 12.652+0.003 eV for H * (3) and 13.338+0.004 eV for H **(4). These values are in good agreement with current theoretical calculations. PACS number(s): 32.80.Fb, 31.50.+w, 32.80.Cy

Shifts of photodetachment thresholds and induced shape resonances ofH−in an electric field

“…4. If we shift the calculated resonance positions by 6 meV such that the lowest resonance coincides with the experimental value 13.338±0.004 eV [11] (the change in the lowest resonance position by the electric field is negligible), the shifted theoretical value for the third resonance is 13.511 eV which is to be compared to the experimental value of 13.513±0.001 eV. In fact, the same calculation shows that the shifted theoretical value for the second resonance position is at 13.467 eV when F=87 kV/cm, which is above the ^P^(-) potential barrier (see Fig.…”

“…4 provide the basis for our interpretation of the experimental data of Halka et al [8]. Earlier studies [9][10][11] have shown that in the zerofield photoabsorption of H~ only states of the ^P^(+) channel are populated. The potential curve for this channel, as shown in Fig.…”

“…The number of channels for a given symmetry converging to the same threshold becomes large when TV is large. For example, for A^=4 and 5 there are seven and nine ^P^ channels, respectively, but only the K >0 channels can support Feshbach resonances and only A = -{• states are dominantly populated in the photodetachment of H-from its ground state {K, T)^ = (0,0)f ^S^ [9,11]. For example, at zero fields the prominent Feshbach resonances below the N=4 threshold [11] belong to (2, l)"*".…”

“…This potential has a maximum barrier at z = [d/FY^^ where its height is shifted from the zero-field threshold by an amount A£ = -f d^/^F^/^. Since only the ^P^(+) states are populated in photoabsorption in the zero field [9][10][11], we take the dipole moment d=18.46 and 37.70 a.u. of the A^=4,5 ^P^(+) channels, respectively.…”

Photodetachment using atom and ion detection

“…Resonances of the type A ¼ À1 have never been observed below H thresholds with n > 2: It is predicted that they are both weaker and much narrower than the corresponding A ¼ þ1 resonance. Halka et al (1991) used photoelectron spectroscopy to study the partial decay of Feshbach resonances lying below the H(n=3,4) thresholds into the H(n=2)+e À continuum.…”