Jong-In Choe

Laser-excitation spectrum and structure of CCl2 in a free-jet expansion from a heated nozzle

Abstract The laser-induced fluorescence excitation spectrum of dichlorocarbene (CCl2) in the region 497–533 nm has been observed in a supersonic free-jet expansion. Analysis of the sub-band structure of near-symmetric roto vibronic bands of the A 1 B 1 ← X 1 A 1 electronic transition has led to vibrational constants for the excited state and rotational constant data for the ground and excited states. A partial structural analysis shows that the CCl2 bond angles are approximately 116° and 136° in the ground and excited electronic states, respectively. Vibrational frequencies in the A state are ω1o = 644 ± 1 cm−1 and ω2o = 308 ± 1 cm−1, and the electronic 0-0 band origin is 16913 ± 3 cm−1.

Microwave spectral study of the axial and equatorial conformers of cyanocyclopentane

Abstract The microwave spectrum of cyanocyclopentane has been observed and analyzed in the 26.5 to 40.0-GHz frequency region. Rotational transitions were assigned for both an axial and an equatorial conformer. These data and those for the molecule deuterated in the 1-position (1- d -cyanocyclopentane) show that both conformers adopt the C s envelope structure. For the normal isotopic species the rotational constants have the following values, in megahertz: axial , A = 4297.196, B = 2210.245, C = 2057.205; equatorial , A = 6324.905, B = 1790.937, C = 1497.792. Relative intensity measurements indicate that the ground-state energy difference of the two conformers is 0 ± 200 cal/mole. The low-frequency (pseudorotational) potential surface has been discussed and compared with that of chlorocyclopentane.

The microwave spectra, conformations, and dipole moments of 4-cyanocyclopentene

Abstract Microwave spectra have been observed and assigned for the axial and equatorial conformations of 4-cyanocyclopentene. For the axial species the rotational constants in megahertz are A = 5095.77, B = 2185.81, and C = 1936.50; for the equatorial species the values are A = 6762.66, B = 1916.72, and C = 1590.60. Dipole moment measurements yielded | μ a | = 3.48 D and | μ c | = 2.51 D for the axial form and | μ a | = 3.85 D and | μ c | = 1.10 D for the equatorial form. Relative intensity measurements showed the equatorial conformer to be 400 ± 60 cal mole −1 lower in energy. Several sets of vibrational satellites were observed and natural abundance C 13 spectra were obtained for the equatorial conformer.

Microwave-microwave double-resonance using a Fabry-Perot cavity spectrometer

The design and operation of a relatively simple, yet versatile spectrometer for microwave–microwave double resonance (MMDR) studies is described. The system consists of a high‐Q, semiconfocal Fabry–Perot cavity resonator which is crossed at right angles by a second free‐space microwave beam. We excite the cavity with a low‐power unmodulated signal source, while the free‐space irradiation source is square‐wave frequency modulated and is of moderately high power (several hundred milliwatts). Both microwave sources are scannable; the signal source is locked to the cavity while the pumping klystron is free running. The signal (cavity) frequency has been operated in the 15–40‐GHz range, and pump frequencies can be selected and easily implemented above or below the signal microwave frequency.