Resonance enhanced multiphoton ionization spectroscopy of carbonyl sulphide

Abstract

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.

The spectroscopy of high Rydberg states of ammonia

“…Both experiments have been described in detail previously 41,42 and so only brief summaries of the two experimental methods are given here.…”

Rotationally resolved photoionization dynamics of hot CO fragmented from OCS

“…As the fragments separate, a strong torque is exerted on the CO fragments, leading to rotationally hot CO. Several photodissociation studies of OCS have been carried out by probing the photofragment product channels, either by laser-induced fluorescence, 2,3 by ion imaging combined with (2ϩ1) REMPI, 4 -7 or by REMPI in combination with photoelectron spectroscopy. [8][9][10] The CO rotational distribution shows a bimodal structure, 2-5,8 -10 with maxima at NЉϭ50 and NЉϭ63. This bimodal distribution is mainly due to two different processes on the 2 1 AЈ ( 1 ⌬) surface, namely direct dissociation and surface crossing to the ground state.…”

Resonance-enhanced multiphoton ionization photoelectron spectroscopy of Rydberg states of N2O below the X 2Π ionization limit

“…If the doubly degenerate bending vibration 2 ϩ is excited, the electronically two-fold degenerate X 2 ⌸ 3/2 and X 2 ⌸ 1/2 spin-orbit components of the ground state ion are split, due to the interaction of the electronic orbital angular momentum ⌳ and the vibrational angular momentum l , which is the so-called Renner-Teller effect. 11 Analysis of emission spectra (X 2 ⌸←A 2 ⌺ ϩ ) of N 2 O ϩ has led to precise energy values for the 2 ϩ ϭ1 vibronic levels. 12 The adiabatic IE for formation of the first excited ionic state A 2 ⌺ ϩ is given as 16.38͑9͒ eV ͑132 185 cm…”

“…Even for Rydberg states relatively close to ͓X 2 ⌸ 3/2 ͔11s, e.g., the ͓X 2 ⌸ 3/2 ͔8s state, the number of vibronic levels which can couple is quite significant. This is partly due to the fact that for the linear N 2 O molecule, Renner-Teller coupling is operative, leading to several vibronic states arising from the coupling between degenerate electronic states and one or more quanta of the bending vibration 2 .…”