An investigation of the torsion-rotation Hamiltonian of CH(3)CF(3) in the ground vibrational state has been carried out using infrared and mm-wave spectroscopy. With infrared Fourier transform spectroscopy, the weak, torsional overtone (v(6) = 2 <-- 0) has been studied leading to the measurement of 382 frequencies between 405 and 440 cm(-1) at a resolution of 0.005 cm(-1). Torsional splittings on the order of 0.03 cm(-1) were observed. With mm-wave methods, a total of 669 rotational transitions between 50 and 360 GHz have been measured at Doppler-limited resolution in the four lowest torsional states v(6) = 0, 1, 2, 3. The experimental uncertainty attained for an isolated line was better than 10 kHz below 150 GHz, and somewhat larger at higher frequencies. For v(6) = 3, torsional splittings as large as 8.7 MHz were observed. The global data set consisted of the current frequency determinations and the 443 measurements with molecular beam, microwave, and mm-wave methods analyzed by I. Ozier, J. Schroderus, S.-X. Wang, G. A. McRae, M. C. L. Gerry, B. Vogelsanger, and A. Bauder [J. Mol. Spectrosc. 190, 324-340 (1998)]. The observation of mm-wave R-branch transitions for v(6) = 1 led to a change in the J-assignment of the forbidden (Deltak = +/-3) transitions reported earlier for this torsional state. A good fit was obtained by varying 24 parameters in a Hamiltonian that represented both the torsional effects and the sextic splittings. In the earlier work, the large reduced barrier height led to high correlations among several of the torsional distortion constants. With the current measurements, many of these correlations are substantially reduced. Improved effective values were determined for the height V(3) of the hindering barrier and the first-order correction V(6) in the Fourier expansion of the potential function. The dipole function which characterizes the transition moment of the torsional overtone (v(6) = 2 <-- 0) can be written as the product of a single effective dipole constant µ(T)(0,eff) and the appropriate off-diagonal matrix element of (1 - cos 3alpha)/2, where alpha is the torsional angle. From an intensity analysis of the infrared spectrum, it has been determined that |µ(T)(0,eff)| = 85.3(62) mD. A novel approach based on a simple regrouping of angular momentum operators is introduced for decoupling the torsional and rotational degrees of freedom. Copyright 2001 Academic Press.
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J Chem Phys
January 2025
Department of Physics and Astronomy, University of Calgary, 2500 University Drive North West, Calgary, Alberta T2N 1N4, Canada.
Spectra of the weakly bound H2O-O2 dimer are studied in the region of the H2O ν2 band using a tunable quantum cascade laser to probe a pulsed supersonic slit jet expansion. These are the first gas-phase infrared spectra of H2O-O2 and among only a few such results for O2-containing complexes. Almost 100 infrared lines are assigned based on the ground state combination differences from the microwave spectrum of H2O-O2.
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January 2025
Terahertz Research Section, Electronics and Telecommunications Research Institute, Deajeon, 34129, Republic of Korea.
The complex dynamics of terahertz (THz) wave scattering by subwavelength-scale structures remain largely unexplored. This article examines the spectral scattering characteristics of subwavelength-sized spherical particles probed by tightly focused THz waves through numerical simulations and experimental techniques. The simulations reveal that the scattering intensity for lower Mie resonance modes (magnetic dipole and electric dipole modes) remains largely unaffected when THz waves are focused down to 0.
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November 2024
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, USA.
Sci Rep
October 2024
Antenna and Sub-Millimeter Wave Section, European Space Agency (ESA), Noordwijk, 2200 AG, The Netherlands.
Remote sensing technologies have the potential to support monitoring of floating plastic litter in aquatic environments. An experimental campaign was carried out in a large-scale hydrodynamic test facility to explore the detectability of floating plastics in ocean waves, comparing and contrasting different microwave and optical remote sensing technologies. The extensive experiments revealed that detection of plastics was feasible with microwave measurement techniques using X and Ku-bands with VV polarization at a plastic threshold concentration of 1 item/m or 1-10 g/m.
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August 2024
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
A combined analysis of millimeter-wave (70-700 GHz) and rotationally resolved infrared (400-1200 cm) spectra of the ground state and seven fundamental vibrational modes of 1-1,2,4-triazole is reported. While the lowest-energy vibrationally excited state (ν) is well-treated using a single-state distorted-rotor Hamiltonian, the second (ν) and third (ν) vibrationally excited states are involved in strong -type Coriolis coupling and require an appropriate two-state Hamiltonian. The oblate nature of 1-1,2,4-triazole is sufficiently close to the oblate symmetric-top limit that the analysis requires the use of A-reduced, sextic centrifugally distorted-rotor Hamiltonian models in the I representation in order to achieve low σ values.
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