Two-photon resonance enhanced MPI-PES above the lowest ionization threshold. Observation of the [a1Δ]5pπ 2Φ state of the SH (SD) radical (original) (raw)
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Chemical Physics Letters, 1995
A (2 + 1) resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) study of the hitherto unobserved [a 1A]5p' rr 2qb Rydberg state of the SH (SD) radical is reported. Despite the fact that this state has an excitation energy which exceeds the lowest ionization energy, ionization is observed to occur preferentially by the absorption of a third photon after the two-photon excitation step, rather than through autoionization. Photoelectron spectra show a large asymmetry in the rotational branching ratios, which is attributed to the high value of A + in the ionic state.
The Journal of Chemical Physics, 1996
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 1 ⌬ or b 1 ⌺ ϩ 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.
The Journal of Chemical Physics, 1997
Experimental and theoretical results on the rotationally resolved photoelectron spectra of the ͓a 1 ⌬͔3d 2 ⌽(vЈϭ0) and the ͓a 1 ⌬͔5 p 2 ⌽(vЈϭ0) Rydberg states of the SH radical are presented. In particular, for the former state, ionization via a large number of members of different rotational branches is considered. The interplay between experiment and ab initio calculations, including alignment, allows for a detailed interpretation of the results. Asymmetries apparent in the rotational ionic distributions and the observed suppression of transitions involving a large change in angular momentum can be explained on the basis of the theory.
The Journal of Chemical Physics, 1997
In this paper, we report the first rotationally resolved one-and two-color resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) study of the HCI molecule. The agreement between our experimental branching ratios and theoretical investigations is excellent. We also report the first zero kinetic energy pulsed field ionization (ZEKE-PFI) experiments carried out in a "magnetic bottle" electron spectrometer. A direct comparison is made between ZEKE-PFI and REMPI-PES spectra for ionization via several rotational levels of the F 1 A2 (Vi = 0) and f 3 A2 (Vi = 0) Rydberg states of HCI. Large differences in both the spinorbit and rotational branching ratios are found between the ZEKE-PFI and REMPI-PES spectra. These differences can be understood qualitatively on the basis of rotational and spin-orbit autoionization mechanisms.
The Journal of Physical Chemistry, 1985
Previously unreported bands of allyl, allyl-& and 2-methylallyl radicals have been detected by mass-resolved, resonance-enhanced multiphoton ionization spectrometry. Focused laser light between 480 and 535 nm induced two-photon absorptions preparing the 3s 2A1 Rydberg states of the radicals. Absorption of two additional photons ionized the excited radicals. These electronic states of allyl and 2-methylallyl radicals lie at 40 085 and 38 369 cm-I, respectively. No subsequent fragmentation of the molecular ions was observed.
Resonance-enhanced multiphoton ionisation spectroscopy of the NH(ND) radical. Part 1?The d 1?+ state
Journal of the Chemical Society, Faraday Transactions, 1991
Rydberg excited states of the OCS molecule in the energy range 70500-86000 cm Ϫ1 have been investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization ͑MPI͒ spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been assisted by companion measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. The present study supports the earlier conclusions of Weinkauf and Boesl ͓J. Chem. Phys. 98, 4459 ͑1993͔͒ regarding five Rydberg origins in the 70500-73000 cm Ϫ1 energy range, attributable to, respectively, states of 3 ⌸, 1 ⌸, 3 ⌬, 1 ⌬ and 1 ⌺ ϩ symmetry arising from the 4p←3 orbital promotion. We also identify a further 21 Rydberg origins at higher energies. These partition into clumps with quantum defects ca. 3.5 and 4.5, which we associate with the orbital promotions np←3 (nϭ5,6), and others with near integer quantum defect which are interpretable in terms of excitation to s,d and ͑possibly͒ f Rydberg orbitals. We also identify MPI resonances attributable to CO(X 1 ⌺ ϩ) fragments and to S atoms in both their ground (3 P) and excited (1 D) electronic states. Analysis of the former resonances confirms that the CO(X) fragments resulting from one photon dissociation of OCS at excitation wavelengths ca. 230 nm are formed with a highly inverted, bimodal rotational state population distribution, whilst the latter are consistent with previous reports of the wavelength dependence for forming ground and excited state S atoms in the near uv photolysis of OCS.
Multiphoton Ionization Spectroscopy of PCl2 Radicals: Observation of Two New Rydberg States
The Journal of Physical Chemistry, 1994
Two new Rydberg states of the PC12 radical were observed using mass-resolved resonance enhanced multiphoton ionization (REMPI) spectroscopy.-The band systems between 440-480 and 380-395 nm are assigned to b 2A1(4sl-X 2Bl and E(4p)-X 2 B~ transitions, respectively. These band systems produc_e signal through 2 + 2(D), and 2 + I@) REMPI processes. Analyses yielded the spectroscopic constants: D 2A1(4s) (uw = 42 760 f 15 cm-l, v'l = 620 f 20 cm-l, and v'2 = 230 f 20 cm-I); E(4p) (vw = 51320 f 10 cm-I, v'l = 600 f 15 cm-I, and u'2 = 240 f 15 cm-l) and 2 2B1 (v"1 = 525 f 10 cm-l). Previously reported infrared absorptions [J. Phys. Chem. 1969,73,2774] are reassigned as v"1 = 525 cm-I and v"3 = 452 cm-l. A b initio calculations yielded the optimized geometries, vibrational frequencies, and ionization potentials of PC12(%B1), PC12+-(AlBl), and PC12+(B3B1). A b initio G 2 calculations predict the adiabatic ionization potential IP,(PCl2) = 8.5 1 eV.
The Journal of Physical Chemistry, 1988
Rydberg excited states of the OCS molecule in the energy range 70500-86000 cm Ϫ1 have been investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization ͑MPI͒ spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been assisted by companion measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. The present study supports the earlier conclusions of Weinkauf and Boesl ͓J. Chem. Phys. 98, 4459 ͑1993͔͒ regarding five Rydberg origins in the 70500-73000 cm Ϫ1 energy range, attributable to, respectively, states of 3 ⌸, 1 ⌸, 3 ⌬, 1 ⌬ and 1 ⌺ ϩ symmetry arising from the 4p←3 orbital promotion. We also identify a further 21 Rydberg origins at higher energies. These partition into clumps with quantum defects ca. 3.5 and 4.5, which we associate with the orbital promotions np←3 (nϭ5,6), and others with near integer quantum defect which are interpretable in terms of excitation to s,d and ͑possibly͒ f Rydberg orbitals. We also identify MPI resonances attributable to CO(X 1 ⌺ ϩ) fragments and to S atoms in both their ground (3 P) and excited (1 D) electronic states. Analysis of the former resonances confirms that the CO(X) fragments resulting from one photon dissociation of OCS at excitation wavelengths ca. 230 nm are formed with a highly inverted, bimodal rotational state population distribution, whilst the latter are consistent with previous reports of the wavelength dependence for forming ground and excited state S atoms in the near uv photolysis of OCS.
Resonance enhanced multiphoton ionisation of the SiF radical: a reinvestigation
Chemical Physics Letters, 1996
We report multiphoton ionisation spectra of ground (X 2H) state SiF radicals, resonance enhanced at the two-photon energy by the v' = 1 level of the C"2E + excited state, at much higher resolution than hitherto. An earlier suggestion by Dulcey and Hudgens that the anomalous intensity of the C"-X (1,0) two-photon transition might be attributable to additional, accidental, resonance enhancement at the one-photon energy by levels of the A2X +, v' ffi 0 state is confirmed, and the double resonance enhancement analysed in detail. A similar accidental double resonance enhancement, involving levels of the A 2X +, v' = 1 state at the one-photon energy, is proposed to explain the observed fragmentary pattern of lines associated with the C' 21-l_X (5,0) two-photon transition.