Microwave spectrum,centrifugal distortion,internal rotation and excited torsional states of isobutene

The microwave spectrum of isobutene has been recorded from 10 to 35 GHz. From the analysis of the ground and first two excited torsional state splittings, the following internal rotation parameters were calculated: V₃ = 2170 cal mol.^?1, V'₁₂ = ?210 cal. mol.^?1, I_α = 3.18amu Ų and angle (methyl-top to b-axis) 58.21°. Centrifugal distortion parameters were also obtained for the ground state.     

Rovibrational Spectroscopy of the v(5) = 1 Level of (28)SiDF(3)

The nu(5) fundamental band of trifluorosilane-d (SiDF(3)) at 627 cm(-1) was studied for the first time by high-resolution FTIR spectroscopy at a resolution of 2.4 x 10(-3) cm(-1). The analysis was performed simultaneously with available microwave and newly measured submillimeter-wave data in the approximation of an isolated degenerate fundamental level of a C(3 Kv) symmetric top molecule leading to a standard deviation of 0.22 x 10(-3) cm(-1) for the reproduction of the infrared wavenumbers, 36 kHz for the microwave, and 198 kHz for the submillimeter-wave frequencies, respectively. The unitary equivalence between the two reductions (Q and D) of the effective Hamiltonian applied in the analysis is demonstrated. Copyright 2000 Academic Press.     

High-Resolution Infrared and Millimeter-Wave Study of the v(3) = 1 State of HSiF(3) and DSiF(3)

Millimeter-wave spectra of HSiF₃ and DSiF₃ in the v₃ = 1 excited state have been measured from 100 to 490 GHz. Infrared spectra have been recorded in the ν₃ regions, ν₀ 424.0301 and 420.9320 cm⁻¹ in HSiF₃ and DSiF₃, respectively, with a resolution of 2.4 × 10⁻³ cm⁻¹. Since in both species the parameters α^B₃ and α^C₃ have very similar values, no K structure could be resolved in the ^QP and ^QR clusters for low-to-medium K values. For high J the effect of the ground state D_JK term more and more dominates and spreads the J clusters into opposite directions such that medium-to-high K components, particularly those with K = 3p, are resolved. Rotational and infrared data have been fitted together using a model up to sextic centrifugal distortion constants. No perturbations were indicated. Hot bands (ν₃ + nν₆)–nν₆ with n = 1, 2, and 3 have been detected and analyzed.     

Microwave spectrum of dimethylallene : Centrifugal distortion analysis

The rotational absorption lines of the molecule dimethylallene in the vibrational ground state deviate from a rigid rotor pattern by shifts due to centrifugal distortion and by shifts and splittings due to methyl top internal rotation. By enlarging the number of previously measured lines it has been possible to apply successfully a Watson-type centrifugal distortion formula and to analyze the resulting “effective rigid rotor” rotational constants for the remaining contributions due to internal rotation and centrifugal distortion. Care has been taken to calculate or at least estimate the separate contributions and compare their magnitudes.     

Rotational and hyperfine constants of CD3I

The rotational spectra of CD₃I (v = 0; v₃ = 1; v₆ = 1) and of ¹³CD₃I in its ground state were observed between 8 and 320 GHz. For the ground state of CD₃I, pure quadrupole resonances were also measured by laser-radiofrequency double resonance. These data have been used to determine with high accuracy the rotational, centrifugal distortion, and hyperfine constants.     

Microwave spectrum of ethyl iodide: Nuclear quadrupole interaction and centrifugal distortion analysis

The microwave spectrum of ethyl iodide has been reinvestigated between 4 and 80 GHz. A total of 181 ground-state transitions with J ≤ 26 and $\text{F ≤}\text{57}\text{2}$ have been analyzed using numerical diagonalization of the quadrupole Hamiltonian. The following rotational and quadrupole coupling constants have been determined (in MHz): A′ = 29 116.321; B′ = 2979.5639; C′ = 2796.4520; χ_aa = ?1478.111; χ_bb = 564.464; χ_cc = 913.648, and χ_ab = 896.38. The quadrupole coupling constants have been transformed to their principal axis system. All the quartic centrifugal distortion constants have been significantly determined, the standard deviation of the fit being only σ = 31 kHz.     

Anharmonic force field of cis- and trans-formic acid from high-level ab initio calculations, and analysis of resonance polyads

The quadratic, cubic, and semidiagonal quartic force fields of cis- and trans-formic acid have been calculated using three different levels of theory. They all give satisfactory results, including the one at the lowest level of theory which is the MP2 method employing a basis set of triple-zeta quality. The results are used to theoretically analyze resonance polyads, including the one involving the 4(1), 5(1), 6(1), 8(1), 7(1)9(1), and 9(2) vibrational states. A semiexperimental equilibrium structure is derived from experimental ground state rotational constants and rovibrational interaction parameters calculated from the ab initio force field. The ab initio structure calculated at the CCSD(T) level of theory using a basis set of quintuple-zeta quality is in excellent agreement with the semiexperimental structure.     

Assignments of submillimeter emissions in difluoromethane pumped by12C18O2 and12C18O2 lasers

A FT spectrum of ₃, ₉ and ₇ of CH₂F₂ is recorded and assigned between 1030 and 1230 cm^–1. Coincidences with CO₂ lasers are investigated.Submillimeter emissions are unambiguously assigned by a loop procedure including only IR and SMM measurements. In some cases pseudo-loops are added using ground state computed energies. In spite of the large perturbations, an exact model for excited vibrational states is not needed to ascertain SMM assignments.