Collision-induced dissociation reactions and pulsed field ionization photoelectron studies

Stimson, Stephanie
Major Professor
Cheuk-Yiu Ng
Committee Member
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The absolute total cross sections for CH2SH+(CH 3S+), CH2S+, HCS+, HS+, CH3+, and CH2 + produced by the collision-induced dissociation (CID) reaction of CH3SH+(12A'') + Ar in the center-of-mass collision energy range of 1--36 eV were measured using a triple-quadrupole double-octopole photoionization apparatus. The relative yields for the product ions formed in the CID reaction, which strongly favor the C-S bond scission process leading to the formation of CH3 + + SH, are significantly different from those measured in previous photoionization and charge exchange studies. The differences in excitation mechanisms for CH3SH+ via collision activation, photoionization, and charge exchange are responsible for the different fragment ion distributions from CH3SH+ observed in these experiments;Using a broadly tunable, high-resolution synchrotron source associated with the Chemical Dynamics Beamline at the Advanced Light Source and a newly implemented PFI-PE experimental scheme, we have obtained the vacuum ultraviolet PFI-PE bands for OCS+(X2 P ), H2+(X2 Sg ), and HD+(X2 S );The vacuum ultraviolet PFI-PE band for OCS+(X 2 P ) in the energy region of 11.09--11.87 eV was measured using high-resolution monochromatic synchrotron radiation. The ionization energies (IEs) for the formation of the (0,0,0) X2 P 3/2 and (0,0,0) 2 P 1/2 states of OCS+ were determined to be 11.1831 +/- 0.0005 eV and 11.2286 +/- 0.0005 eV, respectively, yielding a value of 367 +/- 1.2 cm-1 for the spin-orbit splitting. Using the internally contracted multi-reference configuration interaction approach, three-dimensional potential energy functions for the OCS +(X2 P ) state were generated and used in the variational Renner-Teller calculations of the vibronic states;The rotationally resolved PFI-PE spectra of H2 and HD at a resolution of ≈ 7 cm-1 FWHM (fullwidth-half-maximum) in the photon energy range of 15.30--18.11 eV were obtained. The rotational transitions for the H+2 &parl0;X2S +g, v+ = 0 -- 18) and the HD+( X2 S +, v+ = 0 -- 21) vibronic bands were assigned and then simulated using the Buckingham-Orr-Sichel (BOS) model. From the experimental data, DeltaG(v+ + 1/2), Bv+, and Dv+ were determined and used to calculate the ionic vibrational and rotational constants (oe, oexe , oeye, oeze, Be, and alphae), the internuclear separation (r e), and the dissociation energy (D0).