Two-photon resonance enhanced multiphoton ionization photoelectron spectroscopy of the SH (SD) radical below and above the lowest ionization threshold

Abstract

A two-photon resonance enhanced multiphoton ionization spectroscopic study on the mercapto radical is carried out in the one-photon energy region between 258 and 208 nm. Thirteen previously unobserved Rydberg states converging upon the a 1Δ or b 1Σ+ excited ionic states are reported. Identification and characterization of several states with excitation energies below the lowest ionization limit are performed by analyses of the rotationally resolved two-photon excitation spectra, polarization studies, and photoelectron spectroscopy after excitation of the states. Detailed comparisons between the experimental and simulated excitation spectra, which show for three states clear indications of intensity anomalies, as well as the observation of multiple ionization channels demonstrate that for all states Rydberg–Rydberg and/or Rydberg–valence interactions determine the finer details of their electronic wave functions. Above the lowest ionization limit two-photon resonance enhancement is observed for six Rydberg states. These states are found to ionize by autoionization, rather than by absorption of a third photon. Remarkably, rotationally well-resolved excitation spectra can still be obtained for two of these states. Comparison of the dominant electronic configuration of the six Rydberg states allows us to explain these differences in terms of the possible autoionization channels.

Rotationally resolved multiphoton ionization photoelectron spectroscopy of the [a 1Δ]3dπ 2Φ and [a 1Δ]5pπ 2Φ Rydberg states of the SH radical

“…1 also shows extensive rotational structure. Details of the rotational analyses are given elsewhere; 26 the relevant parameters for this state are summarized in Table I. Figure 2 shows the measured ͑left column͒ and calculated ͑right column͒ photoelectron spectra obtained in a (2 ϩ1) photoionization process via the S 11 (3/2) to S 11 (11/2), S 11 (15/2), and S 11 (19/2) 1 ⌺ ϩ higher ionic state were observed.…”

“…25 In addition, a large number of hitherto undetected Rydberg levels, also with excited ionic cores, have been the subject of a separate publication. 26 When REMPI-PES on radicals is performed with sufficiently high resolution, rotationally resolved studies on these elusive species provide an abundance of detailed information pertaining to the dynamics of the photoionization process under consideration. The first rotationally resolved REMPI-PES study involving the ionic ground state of a radical was carried out on OH.…”

Laser photoelectron spectroscopy: spectroscopy and dynamics of excited states in small and medium‐sized molecules

“…Some of these states are located below the lowest ionization limit, but several are situated above the X3C-ground ionic threshold. A summary of these newly observed states is given in Figure 16 [40,41].…”

“…Simihr to the situation with conventional PES where molecular orbitals became experimentally accessible in a direct way 127-341, laser PES has now developed to the point where orbital interactions between orbitals with different cores can be made experimentally "visible" for the first time. Many examples exist to date in systems as diverse as N [35] and S atoms [36,37], the NH radical [38,39], the SH radical [40,41], N20 [42], NH3 [43,441, methanethiol [45], and dimethyl sulfide [46]. The role of orbital interactions in laser PES will prove to be one of the key elements of the research described in this contribution.…”

Magnetic trapping of SH radicals

“…As explained later, these measures were essential to minimise background H 2 S gas. The photofragments were detected by (2+1) resonanceenhanced multiphoton ionisation (REMPI) using the [a 25 The probe light was generated by a frequency-doubled, Nd:YAG pumped dye laser (Sirah, CobraStretch with Coumarin 503 (307) dye; Continuum, Surelite I-10, 10 Hz repetition rate). Typically 1 mJ of probe light was focussed to an approximate spot size of diameter 200 μm at the centre of the trap to probe via the S 1 (J = 3/2) line at 255.75 nm.…”