(2+1) REMPI spectra of trans- and cis-1, 2-dibromoethylene

(2+1) resonance enhanced multiphoton ionization (REMPI) spectra of jet-cooled 1, 2-dibromoethylene (DBE) are reported for the first time. The spectra are complex because a natural sample contains approximately equimolar amounts of its two geometrical isomers (cis and trans), which have different Rydberg transitions. To this end, the geometric isomers were separated by gas chromatography prior to recording REMPI spectra.;Two spectral regions were examined for trans-1, 2-DBE. The two-photon spectral region between 66800 cm-1 and 70800 cm-1 was examined. A 4pz ← pi Rydberg transition between 66800 and 68000 cm-1 with A g excited state symmetry was characterized. Two 4 f ← pi Rydberg transitions with Bg excited state symmetry and one 4 f ← pi Rydberg transition with Ag excited state symmetry were found between 68000 cm-1 to 70800 cm-1 . All the Rydberg transitions observed in this work belong to series that converge to the first ionization potential (IP) of the molecule. The short vibrational progressions observed involve two totally symmetric in-plane normal modes: C=C-H bending (v3) and C=C-Br bending (v5) with average excited state frequencies of 829 cm-1 and 226 cm-1, respectively.;Similarly, for cis-1,2-DBE one 3dxz ← pi Rydberg transition with A1 excited state symmetry and one 3 d ← pi / 4s ← pi Rydberg transition with A2, B1, or B2 excited state symmetry between 64000 to 66500 cm-1 were characterized. In addition, two 4 f ← pi Rydberg transitions with A1 excited symmetry, one 4d ← pi Rydberg transition with B1, B2, or A2 excited state symmetry, and two 4 p ← pi Rydberg transitions with A2 or B1 excited state symmetry between 67500 and 71500 cm -1 were analyzed. All the transitions were assigned to members of Rydberg series associated with the first IP of the molecule. The short excited state vibrational progressions observed involved three totally symmetric in-plane normal modes: C=C stretching (v2). C=C-H in plane bending (v3) and C-Br stretching (v 4) with average frequencies of 1387 cm-1 1217 cm -1 and 663 cm-1, respectively.;The results of this thesis agree qualitatively with expectations derived from simple molecular orbital arguments regarding the electronic structure of the molecules. The spectra obtained by monitoring Br+ from the dissociation of cis-1, 2-DBE, trans-1, 2-DBE and the mixture are identical which gives information on the C 2H2Br radical produced during the fragmentation.;Keywords: Rydberg states, spectroscopy, resonance enhance multiphoton ionization (REMPI), time-of-flight mass spectrometry (TOF MS), cis -dibromoethylene; trans-dibromoethylene.