17 research outputs found
Librational motion of CO in solid Ar: Raman and IR spectra and quantum simulations
Rovibrational Raman spectra of CO molecules isolated in solid Ar were measured for the 9–30 K temperature
range and compared to past and present IR spectra. The fundamental band appears as a triplet-split structure,
where the center peak shows completely different response to temperature in the Raman and IR spectroscopies.
The peak is sharp and stable in Raman but reversibly broadens beyond recognition in IR upon annealing. The
red-shifted, intense line of the triplet is found thermally inert similarly in both spectroscopies. The third line is
the weakest, and as concentration dependent, it is assigned to a dimer as before. The CO–H₂O impurity complex
is identified as a side band. We employ crystal field and quantum chemical modeling to interpret the disparity
between the spectroscopies. The stable and broadening lines are given assignments to double- and singlesubstitution
sites, respectively. Thermal excitations are not effective in the former case of angularly tightconfined,
deep potential well. In the single-substitutional case, the librational level structure shows up in discriminating
between the Raman and IR selection rules. An effectively ΔJ = 0 totally symmetric transition is found
for Raman that is uncoupled from lattice phonons and corresponding broadening mechanisms. The low-temperature
limit necessitates the use of a fixed lattice approach while the warmer end of the range is best described
with an adiabatic, pseudorotating lattice approach
Ultraviolet-Tunable Laser Induced Phototransformations of Matrix Isolated Isoeugenol and Eugenol
In situ photochemical transformations of monomers of
2-methoxy-4-(prop-1-enyl)phenol
(isoeugenol) and 2-methoxy-4-(prop-2-enyl)phenol (eugenol) isolated
in low temperature matrices were induced by tunable UV laser light,
and the progress of the reactions was followed by FTIR spectroscopy.
Conformer-selective <i>E</i> ↔ <i>Z</i> geometrical isomerizations could be successfully induced by irradiation
at different wavelengths from the 310–298 nm range in the isoeugenol
molecule, contains an asymmetrically substituted exocyclic CC
bond. Photolysis of both studied compounds was also observed, with
H-atom shift from the OH group and formation of two types of long-chain
conjugated ketenes. The photoproduced ketenes were found to undergo
subsequent photodecarbonylation. Interpretation of the observed photoprocesses
was supported by quantum chemical calculations undertaken at different
levels of theory (DFT, MP2, QCISD)
Matrix Isolation FTIR Spectroscopic and Theoretical Study of 3,3-Dichloro-1,1,1-Trifluoropropane (HCFC-243)
The molecular structure and infrared spectrum of the atmospheric pollutant 3,3-dichloro-1,1,1-trifluoropropane (HCFC-243) were characterized experimentally and theoretically. The theoretical calculations show the existence of two conformers, with the gauche (G) and trans (T) orientation around the HCCC dihedral angle. Conformer G was calculated to be more stable than form T by more than 10 kJ mol−1. In consonance with the large predicted relative energy of conformer T, only the G form was identified spectroscopically in cryogenic argon (10 K) and xenon (20 K) matrices prepared from room-temperature equilibrium vapor of the compound. The observed infrared spectra of the matrix-isolated HCFC-243 were interpreted with the aid of high-level density functional theory calculations and normal coordinate analysis. For experimental identification of the weakest IR absorption bands, the spectrum of HCFC-243 in the neat solid state at 145 K was obtained. This spectrum also confirmed the sole presence of the G conformer in the sample. Natural bond orbital and atomic charge analyses were carried out for the two conformers to shed light on the most important intramolecular interactions in the two conformers, in particular those responsible for their relative stability
Identification of the products of partial hydrolysis of silicon tetrafluoride by matrix isolation IR spectroscopy
Ultraviolet-Tunable Laser Induced Phototransformations of Matrix Isolated Isoeugenol and Eugenol
Study on the noncoincidence effect phenomenon using matrix isolated Raman spectra and the proposed structural organization model of acetone in condense phase
Dimers of the Higher-Energy Conformer of Formic Acid: Experimental Observation
We report on the first experimental observation of formic acid dimers composed of two molecules of the higher-energy cis conformer. The cis–cis formic acid dimers are prepared in an argon matrix by selective vibrational excitation of the ground state trans conformer (deuterated form HCOOD) combined with thermal annealing of the matrix at about 30 K. Five cis–cis formic acid dimers are predicted by ab initio calculations (interaction energies from −16.9 to −27.2 kJ molˉ¹), and these structures are used for the assignment of the experimental spectra. Selective vibrational excitation of the obtained cis–cis dimers leads to the formation of several trans–cis dimers, which supports the proposed assignments.peerReviewe