High-resolution infrared spectroscopy of CH281BrF near 8 μm: rovibrational analysis of the ν3 and ν8 fundamentals and resonances with the dark states 2ν5 and ν6 + ν9

The infrared spectrum of isotopically enriched CH₂⁸¹BrF was investigated in the ν₃ and ν₈ region between 1150 and 1370 cm^?1 at a resolution of 0.003 cm^?1. The ν₃ vibration of symmetry species A^′ gives rise to an a-/b-hybrid band with a-type predominance, while the ν₈ mode of A^″ symmetry produces c-type absorption. Due to the proximity of the band origins to those of closely lying overtones and combination bands, the v₃ = 1 and v₈ = 1 levels were found perturbed through Coriolis resonance by the v₅ = 2 (A^′) and v₆ = v₉ = 1 (A^″) states, respectively. The spectral analysis resulted in the identification of 3132 transitions (J^″ ≤ 98 and K_a^″ ≤ 14) for the ν₃ and 2958 transitions (J^″ ≤ 68 and K_a^″ ≤ 19) for the ν₈ bands. The assigned data were fitted using the Watson's A-reduction Hamiltonian in the I^r representation and the perturbation operators. Although no transitions belonging to the perturbers were observed, the band origins and excited state parameters for fundamentals and ‘dark states’ together with coupling terms for the ν₃/2ν₅ and ν₈/ν₆ + ν₉ dyads were determined.     

The high-resolution infrared spectrum of ethylene in the 1800–2350 cm−1 spectral region

Fourier transform spectra of ethylene (C₂H₄) have been recorded in the 1800–2350?cm^?1 (4.3–5.6?µm) spectral region using a Bruker IFS125HR spectrometer at a resolution of 0.004?cm^?1 leading to the observation of six vibrational bands, ν ₇?+?ν ₈, ν ₄?+?ν ₈, ν ₆?+?ν ₁₀, ν ₆?+?ν ₇, ν ₄?+?ν ₆ and ν ₃?+?ν ₁₀. The corresponding upper state ro-vibrational levels were fit using a Hamiltonian matrix accounting for numerous interactions. A satisfactory fit could be obtained using a polyad of nine interacting states {8¹10¹,?7¹8¹,?4¹8¹,?8¹12¹,?6¹10¹,?6¹7¹,?4¹6¹,?3¹10¹,?3¹7¹} of which three (8¹10¹, 8¹12¹ and 3¹7¹) are unobserved dark states. As a result a much more accurate and extended set of Hamiltonian constants were obtained than previously derived. The following band centers were determined: ν ₀(ν ₇?+?ν ₈)?=?1888.9783(20)?cm^?1, ν ₀(ν ₄?+?ν ₈)?=?1958.2850(20)?cm^?1, ν ₀(ν ₆?+?ν ₁₀)?=?2047.7589(20)?cm^?1, ν ₀(ν ₆?+?ν ₇)?=?2178.011(60)?cm^?1, ν ₀(ν ₄?+?ν ₆)?=?2252.8026(24)?cm^?1 and ν ₀(ν ₃?+?ν ₁₀)?=?2171.2397(20)?cm^?1. Finally, a synthetic spectrum that could be useful for ethylene detection in planetary atmospheres was generated.     

Rotation–vibration energy levels from recent potential energy surfaces for the ground electronic states of NO2 and H2O

Using recently published potential energy surfaces, rovibrational energy levels are computed for the ground electronic states of H₂O and NO₂, using three‐dimensional discrete variable representation (DVR) algorithms. Calculations are presented for H₂O to demonstrate the accuracy of these algorithms. In the case of NO₂, comparisons with previous calculations are made as a test for the accuracy of the new potential energy surface. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 535–540, 2000     

Rovibrationally Averaged Nuclear Shielding Constants in OCS

The nuclear shielding constants in OCS are studied using ab initio theoretical methods and gas-phase NMR measurements. The shielding surfaces are calculated and the rovibrational effects and the resulting temperature dependence are analyzed. The temperature dependence of¹³C shielding in the gas phase is determined experimentally in the range 278–373 K.¹³C is the single nucleus for which the experimental data for the temperature dependence can be converted to a reference-independent scale, and good agreement of the measured and calculated ab initio results is observed. For³³S, we discuss a new, more accurate absolute shielding scale.     

Activated barrier crossing: Comparison of experiment and theory

Photochemical isomerization in stilbene and diphenyl butadiene has been studied as a model for activated barrier crossing. Experiments have been carried out from isolated molecule conditions up to 3000 atm pressure in solution-phase samples. The qualitative features predicted by Kramers theory are observed. The system undergoes a transition from energy-controlled to diffusion-controlled behavior in the high-pressure gas phase. The influences of multidimensionality, intramolecular vibrational relaxation, and frequency dependent friction are discussed.Camille and Henry Dreyfus Teacher Scholar.     

High‐resolution stimulated Raman study of the first vibrational hot band of 14N2. Separate observation of the spectra of the ortho and para species.

We present high‐resolution stimulated Raman spectra of the first hot band of nitrogen, ¹⁴N₂, obtained under conditions of low sample pressure and temperature. The use of a Raman optical pumping system allowed us to transfer a significant amount of population to the v = 1 vibrational state, which made possible the observation of the aforementioned hot band with good S/N ratio without resorting to the use of high temperatures or pressures. This has resulted in a more precise and accurate determination of the peak positions than previously existing ones, which in turn has yielded improved values for the molecular constants obtained from the analysis. The rotational selectivity of the pumping process (only one rotational state is initially populated in v = 1), coupled with the negligible probability of nuclear spin interconversion in the time frame of the experiment, has allowed us to observe the hot band spectra of the ortho and para species of ¹⁴N₂ separately. Copyright © 2013 John Wiley & Sons, Ltd.     

Theoretical study of tetrahydrofuran: Comparative investigation of spectroscopic and structural properties between gas and liquid phases

Rovibrational spectroscopic constant of tetrahydrofuran (THF) dimer have been calculated starting from three potential energy curves, each one obtained in a different way: (i) by ab initio calculations at MP2/aug‐cc‐pVDZ level; (ii) using Lennard‐Jones liquid parameters available in the literature, and (iii) from the pair obtained through Monte Carlo Simulation of liquid THF. The comparison among these results allowed the characterization of many solvent effect contributions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011