Search results for "Rotational spectroscopy"
showing 10 items of 53 documents
Exotic SiO(2)H(2) Isomers: Theory and Experiment Working in Harmony.
2016
Replacing carbon with silicon can result in dramatic and unanticipated changes in isomeric stability, as the well-studied CO2H2 and the essentially unknown SiO2H2 systems illustrate. Guided by coupled-cluster calculations, three SiO2H2 isomers have been detected and spectroscopically characterized in a molecular beam discharge source using rotational spectroscopy. The cis,trans conformer of dihydroxysilylene HOSiOH, the ground-state isomer, and the high-energy, metastable dioxasilirane c-H2SiO2 are abundantly produced in a dilute SiH4/O2 electrical discharge, enabling precise structural determinations of both by a combination of isotopic measurements and calculated vibrational corrections. …
Quantum-chemical determination of Born–Oppenheimer breakdown parameters for rotational constants: the open-shell species CN, CO+ and BO
2013
The quantum-chemical protocol for computing Born-Oppenheimer breakdown corrections to rotational constants in the case of diatomic molecules is extended to open-shell species. The deviation from the Born-Oppenheimer equilibrium rotational constant is obtained by considering three contributions: the adiabatic correction to the equilibrium bond distance, the electronic contribution to the moment of inertia requiring the computation of the rotational g-tensor, and the so-called Dunham correction. Values for the Born-Oppenheimer breakdown parameters of CN, CO+, and BO in their (2)sigma(+) electronic ground states are reported based on coupled-cluster calculations of the involved quantities and …
Rotational spectra and hyperfine structure of isotopic species of deuterated cyanoacetylene, DC3N
2008
Abstract Cyanoacetylene enriched in deuterium was used to record pure rotational transitions of DC 3 N and its rare 13 C and 15 N isotopic species by employing Fourier transform microwave (FTMW) spectroscopy on a supersonic-jet expansion at centimeter wavelengths (8.2–25.4 GHz) and by using long-path absorption spectroscopy at millimeter and submillimeter wavelengths (82–900 GHz). In addition, submillimeter wave measurements (304–897 GHz) have been performed for DC 3 N in its v 7 = 1 lowest excited vibrational state. Hyperfine structure caused by the 14 N and D nuclei has been resolved in the FTMW spectra. Quantum-chemical calculations have been performed on the hyperfine structure paramete…
Spectroscopic Detection and Structure of Hydroxidooxidosulfur (HOSO) Radical, An Important Intermediate in the Chemistry of Sulfur-Bearing Compounds
2013
The rotational spectrum of hydroxidooxidosulfur, HOSO, an intermediate of particular interest in the combustion of sulfur-rich fuels, has been determined to high accuracy from gas-phase measurements. Detection of specific isotopic species using isotopically enriched gases suggests that HOSO is formed in our discharge nozzle via the reaction H + SO2 (+M) → HOSO (+M). A precise experimental r0 geometry has also been derived from the isotopic analysis; HOSO has a cis configuration, but the subtle structural question of its planarity remains unresolved. From the derived spectroscopic constants, in situ and remote sensing for this fundamental radical can now be undertaken in a variety of environ…
Controlling molecular alignment rephasing through interference of Raman-induced rotational coherence
2000
0021-9606; Quantum control over molecular alignment rephasing is experimentally investigated in gaseous CO2. The control process is achieved by illuminating the medium with a pair of pump-pulses separated in time by approximately an integer value of T0=1/8B(0), where B(0) is the rotational constant. Through a Raman-type process, each pulse alone produces rotational coherence leading to a periodic orientational anisotropy. It is the combination of the two pulses that yields to quantum interference, resulting in a modification of this anisotropy probed by a third delayed pulse. The effect is accurately analyzed for different time delays between the two pulses. A theoretical analysis supplies …
Ab initio calculations on the molecular structure of fluorocyanopolyynes
1998
Abstract The molecular structure of the first three members of the fluorocyanopolyynes was studied by ab initio Hartree-Fock calculations with a polarized double zeta basis set and at MP2 level with the same basis set. Alternating triple and single bonds were found; a theoretical estimate of rotational constants and dipole moments was performed and a comparison with the available experimental data was made. An analysis of the theoretical vibrational frequencies of the title compounds was carried out.
A MRCI PS and CASSCF study of the ground state MgO dissociation energy
1991
Abstract Ab initio calculations at CASSCF and MRCI PS levels are used to determine the dissociation energy for the X 1 Σ + state of MgO, which adiabatically dissociates to the ground state 1 S g of magnesium and to the excited 1 D g state of oxygen, as well as other spectroscopic parameters. Emphasis is placed upon the problem of properly selecting an adequate active space in CASSCF calculations and upon the improvements obtained in MRCI by selecting perturbatively the most important contributions to the total wavefunction and evaluating the remaining ones only by perturbational method. Through a procedure based on stabilizing the computed dissociation energy, values of 3.87 eV (MRCI PS) an…
The equilibrium structure of trans-glyoxal from experimental rotational constants and calculated vibration–rotation interaction constants
2003
A total of six high-resolution FT-IR spectra for trans-glyoxal-d2, trans-glyoxal-d1 and trans-glyoxal-13C2 were recorded with a resolution ranging from 0.003 to 0.004 cm−1. By means of a simultaneous ground state combination difference analysis for each of these isotopologues using the Watson Hamiltonian in A-reduction and Ir-representation the ground state rotational constants are obtained. An empirical equilibrium structure is determined for trans-glyoxal using these experimental ground state rotational constants and vibration–rotation interaction constants calculated at the CCSD(T)/cc-pVTZ level of theory. The least-squares fit yields the following structural parameters for trans-glyoxal…
Theoretical spectroscopic parameters of the alkali monofluorides LiF, NaF and KF
1992
Abstract Multireference configuration interaction and second-order perturbation theory are used to determine accurate spectroscopic parameters for the ground state of the alkali monofluorides from LiF to KF. Systematic saturation of the spdf subspaces of the atomic basis sets for the electron affinity of fluorine and the ionization potential of the metals have been shown to be more efficient than for the approximate dissociation energies in the molecule. the calculated rotational and vibrational constants and transitions for the three systems show excellent agreement with the expeirmental data.
Rotational spectrum and equilibrium structure of silanethione, H2SiS
2008
Unsubstituted silanethione, H(2)Si=S, has been characterized experimentally for the first time by means of rotational spectroscopy; the equilibrium structure of this fundamental molecule has been evaluated through a combination of experimental data from a total of ten isotopologues and results of high-level coupled-cluster calculations.