Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy.
A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (nu1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and CS2 are discussed.
The optical double resonance spectrum of the B̃1A1 state of Cl2CS
Abstract The technique of optical optical double resonance is used to produce vibrationally simplified spectra of the B 1 A 1 state of Cl2CS. Previous work on the extensive B 1 A 1 - X 1 A 1 absorption spectrum had been hampered by the many long, overlapped progressions which arise from the large geometry change on excitation. Much clearer assignments are obtained in this study. The B 1 A 1 state origin is found to lie at 33991 cm−1. The three a1 vibrations (212, 249, and 340 cm−1) and one b2 vibration (292 cm−1) have been determined for the excited state.
Core extraction for measuring state‐to‐state differential cross sections of bimolecular reactions
We describe a method we call core extraction for measuring the speed distributions of products from photoinitiated bimolecular reactions for the purpose of determining state‐to‐state differential cross sections. Core extraction is demonstrated by determination of the state‐to‐state differential cross section for the reaction Cl+CH4(υ3=1)→HCl(υ=1, J=1)+CH3. The method of core extraction measures three‐dimensional projections of the velocity distribution using a time‐of‐flight mass spectrometer equipped with a mask to reject off‐axis scattered products. This three‐dimensional projection is then converted to a state‐to‐state differential cross section via simple transformations. Competition between instrumental resolution and signal in core extraction is discussed, and the behavior of our system is checked with simple velocity distributions that result from photodissociation of Cl2. Core extraction is compared with other methods for the measurement of state‐resolved differential cross sections.