Chiao-Wei Chen

Photodissociation of CFX=CHCl (X=H,F) at 193 nm by product translational spectroscopy

In this work, we have studied the photodissociation of CFX=CHCl (X=H,F) at 193 nm using product translational spectroscopy. Results show that while the photoelimination of fast Cl, slow Cl, HCl, and HF occurs for both molecules, the cleavage of the C=C bond is only measurable for CF2=CHCl. Among these, only the fast Cl product was detected with strong angular preference with respect to polarized laser light. Product translational energy distributions P(Et) were measured for all dissociation channels. The difference in the P(Et) distributions between three-centered (3C) and four-centered (4C) molecular elimination reactions was observed. The low recoil energy for 3C HCl elimination from CF2=CHCl strongly suggests that there is no concerted isomerization from :C=CF2 to FC≡CF. Although we detected no primary C–F bond fission in the present study, a relatively large yield of the secondary dissociation products F+C2H2 was determined for the internally excited fluorovinyl radical CHCHF. The results are discusse...

Electronic bands of scandium monocarbide, ScC, in the region 14 140–16 000 cm−1

Scandium monocarbide molecules, ScC, have been prepared by the reaction of 532 nm laser-ablated Sc metal with acetylene or methane under supersonic jet-cooled conditions. Electronic spectra of Sc12C and Sc13C have been recorded in the region 14 140-16 000 cm-1 using laser-induced fluorescence, and about 40 bands of each isotopomer have been analyzed rotationally. Wavelength resolved emission spectra have been obtained for many of them. The results show that Sc12C has a 2Πi ground state, with a bond length of 1.952 Å. Its vibrational frequency and spin-orbit coupling constant are 648 cm-1 and -39.47 cm-1, respectively (631 cm-1 and -39.32 cm-1 in Sc13C). Lying 155.58 cm-1 above the X2Π3/2 level (154.72 cm-1 in Sc13C) is a 4Π5/2 level, the lowest spin-orbit component of a 4Πi state. The excited states at higher energy are very complicated. Bands from both the doublet and quartet spin manifolds are present, and there are strong doublet-quartet interactions which induce many nominally-forbidden bands violating the selection rule ΔS = 0. Eight excited electronic states have been recognized, including four 4Δ states. These 4Δ states represent four of the five 4Δ states from the electron configurations (C 2pσ)2 (C 2pπ)2 (Sc 3dδ)1 and (C 2pσ)1 (C 2pπ)2 (Sc 4sσ)1 (Sc 3dδ)1.

THE LOW-LYING ELECTRONIC STATES OF SCANDIUM MONOCARBIDE, ScC

Extensive wavelength-resolved fluorescence studies have been carried out for the electronic bands of ScC and ScC lying in the range 14000 16000 cm−1. Taken together with detailed rotational analyses of these bands, these studies have clarified the natures of the low-lying electronic states. The ground state is an Ω = 3/2 state, with a vibrational frequency of 648 cm−1, and the first excited electronic state is an Ω = 5/2 state, with a frequency of 712 cm−1, lying 155.54 cm−1 higher. These states are assigned as the lowest spin-orbit components of XΠi and aΠi, respectively. The quartet nature of the a state is confirmed by the observation of the Π3/2 component, 18.71 cm−1 above the Π5/2 component. The strongest bands in the region studied are two ∆7/2 Π5/2 transitions, where the upper states lie 14355 and 15445 cm−1 above XΠ3/2. Extensive doublet-quartet mixing occurs, which results in some complicated emission patterns. The energy order, aΠ above XΠ, is consistent with the ab initio calculations of Kalemos et al.,a but differs from that found by Simard et al in the isoelectronic YC molecule.b