Rovibrational Interaction Research Articles

Millimeter-wave and high-resolution FTIR spectroscopy of [formula omitted]: the ground and [formula omitted] states

The first high-resolution infrared spectroscopic study of the ν 4 band at 322.85 cm - 1 of SiH 2 F 2 is reported, and millimeter-wave spectra in the 350–471 GHz range of the ground and the v 4 = 1 excited states are presented. These data have been combined with existing microwave measurements and substantially improved ground state parameters, and molecular constants of the v 4 = 1 state, have been determined. The quadratic, cubic, and semidiagonal quartic force field of difluorosilane has been calculated at the MP2 level of theory employing a basis set of polarized valence triple-zeta quality. The spectroscopic constants derived from the force field are in excellent agreement with experiment. The equilibrium structure has been derived from experimental ground state rotational constants and ab initio rovibrational interaction parameters. This semiexperimental structure is in perfect agreement with the ab initio equilibrium geometry calculated at the CCSD(T) level of theory.

The Equilibrium Structure of Silyl Fluoride

The experimental equilibrium structure of silyl fluoride has been determined using new sets of accurate rotational constants that have recently been obtained by taking into account the most important interactions between the excited vibrational states. The equilibrium structure has also been calculated at the CCSD(T) level of theory with the cc-pVQZ+1 basis set (including corrections for the core correlation). The anharmonic force field up to semidiagonal quartic terms has been calculated at the MP2 level of theory and the equilibrium structure has been derived from the experimental rotational constants and the ab initio rovibrational interaction parameters. Finally, the average structure of both 28SiH 3F and 28SiD 3F has been reevaluated and used to derive the equilibrium structure. These structures are compared and the experimental structure is found to be in slight disagreement with the other ones. The preferred structure is obtained by calculating the median value of the different structures. The results are r e(SiF)=1.5907 (9) Å, r e(SiH)=1.4696 (13) Å, ∠ e(HSiF)=108.32(15)°, and ∠ e(HSiH)=110.60(14)°.

Anharmonic force field, structure, and thermochemistry of CF2 and CCl2Electronic supplementary information (ESI) available: Force constants and thermochemical properties of CF2 and CCl2. See http://www.rsc.org/suppdata/cp/b2/b202865d/

The anharmonic force field up to quartic terms has been calculated for both CF2 and CCl2 at the CCSD(T) level of theory with large basis sets. The calculated spectroscopic parameters are in excellent agreement with the available experimental data. The equilibrium structure of CCl2 has been calculated at the CCSD(T) level of theory with the cc-pV5Z basis set (including core correlation corrections). It is in excellent agreement with the semi-experimental equilibrium structure derived from the experimental rotational constants and the ab initio rovibrational interaction parameters. The heats of formation of CF2 and CCl2 have been calculated using the W2 method and are −193.43 and 227.96 kJ mol−1, respectively.

Ab initio anharmonic force field, spectroscopic parameters and equilibrium structure of trifluorosilane

The quadratic, cubic and semidiagonal quartic force field of trifluorosilane has been calculated at the MP2 level of theory employing a basis set of polarized valence triple-zeta quality. This force field has been used to predict the spectroscopic constants, including the parameters specific of the double degenerate vibrational states. The calculated values are found to be in good agreement with the available experimental data, and explanations are offered for discrepancies. This confirms the accuracy of the ab initio force field and the validity of the theory of the reduction of the rovibrational Hamiltonian of a doubly degenerate vibrational state. The equilibrium structure has been derived from the experimental rotational constants and the ab initio rovibrational interaction parameters. This semiexperimental structure is in excellent agreement with the ab initio equilibrium geometry.

Ab initio potential energy surface and rovibrational states of HBO

The potential energy surface describing the large-amplitude motion of H around the BO core in the HBO molecule has been determined from ab initio calculations. This surface has been sampled by a set of 170 grid points from a two-dimensional space defined by the stretching and the bending coordinates of the H nucleus. At each grid point, the BO bond length has been optimized using the second-order Møller–Plesset perturbation theory with the basis set aug-cc-pVTZ. The surface has a local minimum for the linear as well as the bent configuration of HBO. A low energy barrier to the linear configuration BOH causes a large-amplitude motion and a strong rovibrational interaction in the molecule. Its rovibrational dynamics is different from the dynamics in bent or quasilinear triatomic molecules.

Ab initio study and millimeter-wave spectroscopy of P2O

The millimeter-wave spectrum of P2O produced by reacting P4 vapor with atomic or molecular oxygen directly inside the absorption cell has been observed in 13 vibrational states. Reliable identification of the various vibrationally excited states has been achieved with the help of high-level ab initio calculations resulting in accurate geometric data and an anharmonic force field. Careful analysis of the vibrational levels observed resulted in 13 sets of rotational and centrifugal distortion parameters, which have been used, in turn, to determine the equilibrium rotational, quartic centrifugal distortion, and rovibrational interaction constants of P2O. The 2ν1−ν3 Fermi resonance has been analyzed.

The equilibrium structure of silene H2C=SiH2 from millimeter wave spectra and from ab initio calculations

Silene, H2CSiH2, has been efficiently produced by pyrolysis of 5,6-bis(trifluoromethyl)- 2-silabicyclo[2.2.2]octa-5,7-diene (SBO). Seven isotopomers have been observed by millimeter- and submillimeter-wave spectroscopy. From the different sets of experimental molecular parameters and from ab initio calculations of the rovibrational interaction parameters, the equilibrium structure has been obtained by a least squares analysis of the rotational constants. The results are: re(Si=C)=1.7039(18) Å, re(C–H)=1.0819(12) Å, re(Si–H)=1.4671(9) Å, ∠HCSi=122.00(4)°, and ∠HSiC=122.39(3)°. This experimental structure is in excellent agreement with the equilibrium geometry calculated at the CCSD(T) level of theory with a cc-pV(Q,T)Z basis set. This is the first experimental determination without any constraint of the Si=C double bond length in the parent compound of the silaalkene family. A lifetime of 30 ms has been observed for this molecule in the gas phase at low pressure.

The infrared spectrum of the ν2 fundamental band of the molecular ion

The observation and analysis of 46 lines of the infrared ν2 band of the [Formula: see text] molecular ion are described. The data include 16 new observations as well as the 30 previously published lines. The spectra are observed in absorption in a hydrogen discharge using tunable monochromatic sources, either a laser difference-frequency system or a diode laser. Two modulation techniques, either discharge amplitude modulation or Doppler velocity modulation, are used to increase the sensitivity. Ground state combination differences between the observed lines are in good agreement with ab initio calculations, and scaled ab initio rotational term values are used to relate the different K-energy stacks. Padé-type expressions are found useful in representing the line frequencies, and 44 lines are fitted by 23 parameters with a standard deviation of 0.014 cm−1. The two lines omitted appear to be perturbed by a rovibrational interaction between the ν2 and ν1 states that should become more important for higher values of J.