Journal of Molecular Spectroscopy最新文献

We observed ten pseudo a-type transitions in the E state of N-ethylacetamide (NEAA) using a Fourier transform microwave spectrometer. We found triplets caused by the coupling between the two methyl groups for the observed pseudo a-type transitions. Also, we succeeded in observing similar triplets for the 5 a-type Q-branch transitions, 20 b-type and 7 c-type transitions of the E state of NEAA. These observed triplets allowed us to determinate the potential barrier V₃ to internal rotation of the ethyl-methyl group to be 1078 (12) cm⁻¹. In addition, though the observed intensities of the c-type transitions in the A state were weak, the c-type transition in the E state were observed to be as intense as the b-type transitions of the E state. We explained in this paper the abnormal intensities of the c-type transitions and pseudo a-type transitions in the E state of NEAA.

Cantilever-enhanced Photoacoustic Spectroscopy in combination with Wavelength Modulation Spectroscopy was used for the multicomponent analysis of gases. Distributed feedback Quantum Cascade Laser tunable in the region of ∼ 1045 – 1048 cm⁻¹ was used as the excitation source. Principal component analysis (PCA) and Partial Least Squares (PLS) (the pls package in the statistical software R) methods were applied to a mixture of selected substances (methanol and ethanol) in the gas phase to both simulated (www.spectraplot.com) and experimentally acquired spectra, PCA predicting the number of substances and PLS its concentrations.

Line strengths and line shape parameters of Ar- and N₂-perturbed CO₂ R-branch transitions (82 $\le J^{″}\le$ 90) in the ${\nu }_3$ fundamental band were measured in a shock tube from 730 K to 2500 K and pressure below 1.13 atm using laser absorption spectroscopy (LAS). The retrieved absorption curves were fitted with the Voigt and the quadratic speed-dependent Voigt (qSDV) profiles to obtain the line strengths, broadening, and shift coefficients. Line strengths were compared to values in HITEMP, HITRAN2020, and Ames2021 databases, and the HITEMP shows the best agreement with the measured results. Ar- and N₂-broadening and shift coefficients were regressed into the power law and the double power law form to study the temperature dependence of the targeted lines. The speed-dependence parameter $a_w$ was temperature-dependent. The J-dependence of the derived broadening and shift coefficients was discussed. The results of this work will aid the development of the absorption model in the far-wing region and the design of CO₂ LAS sensors for high-temperature measurement.

New analysis and spectra are reported for the gas-phase ammonia-formic acid complex. Calculations to determine the theoretical barrier to internal rotation were conducted and led to the new internal rotation analysis of the dimer. Using the new analysis and calculations, 12 new lines were measured and assigned and included in the present analysis. This is the first internal rotation analysis for this complex. The measurements were made in the 7–22 GHz range using two Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometers. The complex was analyzed as a hindered rotor and 20 A and 16 E state transitions were fit with the XIAM5 program. The rotational constants were determined to have the following values: A = 11970.19(9) MHz, B = 4331.479(4) MHz, and C = 3227.144(4) MHz. Rotational constants, quadrupole coupling constants, and internal rotor parameters were fit to the spectrum. Double resonance was used to verify line assignments and access higher frequencies. The barrier to internal rotation was found to be 195.18(7) cm⁻¹. High level calculations are in good agreement with experimental values. The calculated V₃ barrier values range from 168.3 to 212.8 cm⁻¹.

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue ¹³CD₂NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm⁻¹) in the 500–4000 cm⁻¹ region, and high resolution (0.00096 cm⁻¹) in the 280–500 cm⁻¹ region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the ${\nu }_{12}$ band of ¹³CD₂NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type ${\nu }_{12}$ band were assigned and fitted using the Watson's A-reduced Hamiltonian in the I^r representation to derive its band center and the $v_{12}$ = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm⁻¹. The band center of the ${\nu }_{12}$ band of ¹³CD₂NOH were found to be 391.054446(36) cm⁻¹. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the ${\nu }_{12}$ band of ¹³CD₂NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm⁻¹. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the $v_{12}$ = 1 state of ¹³CD₂NOH were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rovibrational constants of ¹³CD₂NOH for both ground and $v_{12}$ = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of ¹³CD₂NOH in the 280–4000 cm⁻¹ region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the ${\nu }_{12}$