Posts Tagged ‘Ar matrix’
Quantum Chemical Study on HKrC5N, HXeC5N, and Related Rare Gas Compounds
The recent identification of HRgC5N (Rg = Kr, Xe) in a cryogenic matrix calls for an in-depth theoretical study on these compounds. Here we present the results of CCSD(T), MP2, and DFT calculations concerning the molecular structure, stability, and vibrational spectroscopy. The procedure combining CCSD(T) calculations for variable H–Rg distances with the anharmonic description of the corresponding stretching vibration, based on a Morse-type potential energy function, was proposed and has led to good agreement between computational and experimental values for H–Rg stretching frequencies, at relatively low computational costs. High Raman scattering activity of HRgC5N and of its isomers, predicted at the DFT level, gives some prospects for the detection of these molecules with a method alternative to the IR absorption spectroscopy.
Electronic absorption and phosphorescence of cyanodiacetylene
Electronic absorption and emission spectra have been investigated for cyanodiacetylene, HC5N, an astrophysically relevant molecule. The analysis of gas-phase absorption was assisted with the parallel rare gas matrix isolation experiments and with density functional theory (DFT) predictions concerning the excited electronic states. Mid-UV systems: B1Δ←X1Σ+ (origin at 282.5 nm) and B1Σ–←X1Σ+ (306.8 nm) were observed. Vibronic assignments have been facilitated by the discovery of the visible phosphorescence a3Σ+←X1Σ+ in solid Ar, Kr, and Xe. Phosphorescence excitation spectra, as well as UV absorption measurements in rare gas matrices, revealed the enhancement of A←X transitions. The vibronic structure of dispersed phosphorescence spectra supplied new data concerning the ground state bending fundamentals of matrix-isolated HC5N. The experimental singlet-triplet splitting, 2.92 eV in Ar, closely matches the value of 3.0 eV predicted by DFT.
The C3N− anion: First detection of its electronic luminescence in rare gas solids
The 193 nm laser irradiation of cyanoacetylene HCCCN that was isolated in rare gas solids led to a long-lived luminescence origin at 3.58 eV, which was assigned to the a 3Σ+-X 1Σ+ system of cyanoacetylide CCCN−. The identification, which involved 15N and 2H isotopic substitution studies, is based on vibronic spacings in the phosphorescence spectrum compared to previous infrared absorption measurements and to theoretical results regarding CCCN− vibrational frequencies, as well as on a BD(T)/cc-pVTZ prediction for the singlet-triplet energy gap in this anion 3.61 eV. The same emission was also generated from Kr/HC3N mixtures subjected to a glow electric discharge immediately before the solidification cold-window-radial-discharge technique.
Full text: J. Chem. Phys. 128 (2008) 164304
Matrix isolation IR spectroscopic and ab initio studies of C3N− and related species
Coupled cluster calculations were carried out for C3N−, CCNC−, C3N, CCNC, C3N+, and C3O. They support the experimental identification of the C3N− ion by means of matrix isolation infrared IR spectroscopy. The anion was generated in electric discharges through the cyanoacetylene isotopomers HC314N, HC315N, and 2HC3N, trapped in cryogenic rare gas matrices Ne, Ar, Kr, anddetected via its two most intense IR absorption bands, assigned to the 1 and 2 stretching vibrations. C3N− appears to be quite a stable anion, with a vertical detachment energy predicted to be as high as 4.42 eV. A large equilibrium electric dipole moment of 3.10 D facilitates the investigation of C3N− by microwave spectroscopy and radio astronomy. Various structural parameters and spectroscopic properties have been calculated for all tetra-atomic species considered.
Full text: J. Chem. Phys 128 (2008) 154305
Spectroscopy of cyanodiacetylene in solid argon and the photochemical generation of isocyanodiacetylene
Following the measurements of UV and mid-IR spectra of cyanodiacetylene, H-CC2-CN, isolated in low temperature Ar matrices, the first photochemical study on this compound and on its 2H isotopomer was carried out with the laser light tuned to 267 nm and with far-UV discharge lamps. Evidence for the formation of isocyanodiacetylene, H-CC2-CN, was found in infrared absorption spectra interpreted with the aid of available theoretical predictions.
Full text: J. Chem. Phys. 126 (2007) 164301
