The ν5 and ν3 Raman bands of CH2D2

The ν₅ and ν₃ Raman bands of CH₂D₂ have been recorded with a resolution of 0.35 cm^?1. The ν₃ state is well known from infrared studies. Three hundred twenty-nine transitions of the ν₅ band were analyzed, assuming an unperturbed upper state, giving a standard deviation on the fit of the upper-state energies of 0.037 cm^?1, The constants A, B, C, Δ_J, Δ_JK, and Δ_K differed significantly from the ground-state values, and ν₅ was determined as 1331.41 ± 0.05 cm^?1. This work represents the first complete analysis of the fine structure of a rotation-vibrational Raman band for an asymmetric rotor. The ν₅ state could not be analyzed in infrared so this investigation, once more, demonstrates the usefulness of the Raman method.     

Infrared rotation-vibration spectra of ethane: The perpendicular band, ν7, of C2H6

The study of the gas-phase infrared spectrum of C₂H₆ in the region of the perpendicular CH-stretching band, ν₇, near 3000 cm^?1 is extended for the ΔK = + 1 subbands as far as K = 20. The spectral resolution of ～0.030 cm^?1 is increased to ～0.015 cm^?1 by deconvolution. The earlier investigation of this band for KΔK = +9 to ?5, is repeated with greater accuracy, providing more reliable ground-state constants (cm^?1): B₀ = 0.663089 ± 24, D₀^J = (0.108 ± 4) × 10^?5, D₀^JK = (0.50 ± 7) × 10^?5. The molecular constants (cm^?1) for the ν₇ fundamental are B₇ = 0.66310 ± 3, A₇ = 2.682, ν₀ = 2985.39, ζ₇ = 0.128. A discussion of resonance effects in this band, in particular x-y-Coriolis and Fermi resonance, is given.     

Diborane : High resolution infrared rovibration studies of B2H6 and B2D6

Ground state rotation and quartic distortion constants were obtained for ¹¹B₂D₆ from the analysis of high resolution (0.05 cm⁻¹) Fourier transform infrared spectra. The bands studied comprised the ν₁₇, ν₁₈ type A, and ν₁₄, ν₉ + ν₁₅ type C bands of ¹¹B₂H₆ and the ν₁₆, ν₁₇, ν₁₈ type A, ν₈ type B, and ν₁₄ type C bands of ¹¹B₂D₆. In the case of ¹¹B₂H₆, the authors' ground state data were combined with those of Lafferty et al. obtained from a previous study (J. Mol. Spectrosc. 33, 345–367 (1970)) at comparable resolution of the ν₁₆ type A and ν₈ type B fundamentals. Information on the ground state rotational energy manifold of ¹¹B₂H₆ was accumulated up to J = 23, K_a = 18, and of ¹¹B₂D₆ up to J = 32, K_a = 22. This permitted rather precise determination of the distortion constants Δ_J⁰, Δ_JK⁰, Δ_K⁰, although δ_J⁰ and δ_K⁰ proved to be too small (< 10⁻⁷ cm⁻¹) and were constrained to values calculated from the force field. Sets of upper state parameters were determined for all vibrational levels studied. Although these appear to be essentially unperturbed globally, several localized perturbations were observed and identified.     

Analysis of the ν6(A″2) band of cyclopropane-d6 recorded under high resolution

The parallel band ν₆(A″₂) of C₃D₆ near 2336 cm^?1 has been studied with high resolution (Δν = 0.020 – 0.024 cm^?1) in the infrared. The band has been analyzed using standard techniques and the following parameters have been determined: B″ = 0.461388(20) cm^?1, D″_J = 3.83(17) × 10^?7 cm^?1, ν₀ = 2336.764(2) cm^?1, α^B = (B″ ? B′) = 8.823(12) × 10^?4 cm^?1, β^J = (D″_J ? D′_J) = 0, and α^C = (C″ ? C′) = 4.5(5) × 10^?4 cm^?1.     

Vibration-rotation spectra of ethane and deuteroethanes: The ν2 band of CH3CD3

The ν₂ band of CH₃CD₃ has been measured under an effective resolution of 0.04 cm^?1. About 400 transitions observed in the region from 2130 to 2060 cm^?1 have been identified as due to the ν₂ fundamental band. The least-squares analysis of these transitions yields the band constants: ν₀ = 2089.957, B′ = 0.548937, D_J′ = 6.97 × 10^?7, D_JK′ = 1.92 × 10^?6, A′ - A″ = ?0.01158, and D_K′ - D_K″ = 1.30 × 10^?6 cm^?1. The ground-state constants B″, D_J″, and D_JK″ are fixed to the values obtained from microwave spectroscopy.     

Tunable laser study of the ν10 + ν11 band of cyclopropane

Diode laser measurements of the ν₁₀ + ν₁₁ (l_tot = ±2) perpendicular band of cyclopropane have led to the assignments of roughly 600 lines in the 1880–1920-cm^?1 region. Most of the spectra were recorded and stored in digital form using a rapid-scan mode of operating the laser. These spectra were calibrated, with the aid of a computer, by reference to the R lines of the ν₁ + ν₂ band of N₂O. The ground state constants we obtained are (in cm^?1) B = 0.670240 ± 2.4 × 10^?5, D_J = (1.090 ± 0.054) × 10^?6, D_JK = (?1.29 ± 0.19) × 10^?6, D_K = (0.2 ± 1.1) × 10^?6. The excited state levels are perturbed at large J values, presumably by Coriolis couplings between the active E′(l_tot = ±2) and the inactive A′(l_tot = 0) states. Effective values for the excited state constants were obtained by considering only the J < 15 levels. The A₁-A₂ splittings in the K′ = 1 excited states were observed to vary as q_effJ(J + 1), with q_eff = (2.17 ± 0.17) × 10^?4 cm^?1.     

Diode laser spectra of the ν2 band of H212CO and H213CO

The Q-branches of the ν₂ (CO stretch) band of H₂¹²CO and H₂¹³CO have been studied in high resolution using an infrared diode laser. Accurate upper state constants, including A, B, C, Δ_J, Δ_JK, Δ_K, and H_K, were determined from an analysis of the data for 97 lines of H₂¹²CO and 79 lines and H₂¹³CO and compared with previous reported values. Band centers were also determined and reported as 1746.009 ± 0.002 cm^?1 for H₂¹²CO and 1707.981 ± 0.002 cm^?1 for H₂¹³CO.     

The ν6 parallel band of cyclopropane at 3100 cm−1

The ν₆ fundamental of cyclopropane has been recorded on a 4.5-m vacuum spectrometer. Deconvolution of the spectrum has revealed considerably more detail than found in previous investigations. New information of a qualitative nature has been learned about the highly perturbed upper state and improved values of the band center and the upper-state rotational constant have been obtained. A lower-state combination-difference analysis using J values up to J = 23 has resulted in values of B″ and D″_J which are in excellent agreement with recent investigations. The following values of molecular constants, in wavenumber units (cm^?1), have been determined: B″ = 0.67023, D″_J = 0.93 × 10^?6, ν₀ = 3101.529, and B′ ? B″ = ?0.0019. The present data have been used with data from recent Raman and infrared spectra of C₃H₆ in a combined least-squares fit to the ground-state constants.     

Diborane: High-resolution infrared rovibration studies of 10B2D6

Studies of five comparatively unperturbed infrared active bands in the spectrum of ¹⁰B₂D₆ were undertaken with a resolution of ca. 0.05 cm^?1. These comprise three type-A bands (ν₁₇, ν₁₈, and ν₅ + ν₁₅), one type-B band (ν₈), and one type-C band (ν₁₄). Ground-state rotational and quartic centrifugal distortion constants were determined for the first time from a total of over 400 combination differences. Sets of upper-state parameters were determined for all five bands studied, and the effects of a number of minor Coriolis interactions between fundamental vibrations are discussed.     

Vibrational spectra and force constants of symmetric tops: Rovibrational spectra in the ν3 region of monoisotopic species of H3GeCl,H3GeBr,and H3GeI

The gas phase infrared spectra of several monoisotopic species of H₃GeCl, H₃GeBr, and H₃GeI have been recorded in the ν₃ region near 420, 300, and 250 cm^?1, respectively, with a resolution between 0.03 and 0.04 cm^?1. Rotational J structure of the fundamental and of several “hot” bands of ν₃ has been resolved and analyzed by means of polynomial methods. The K structure of J clusters is indicated, and α₃^A values were estimated from a band contour simulation. The molecular parameters ν₃⁰, χ₃₃, (B₃-B₀), and $\text{D}{}_{\mathrm{J}}$ were determined for several isotopic combinations. The ν₃ and 2ν₃ levels are apparently unperturbed except for H₃Ge³⁵Cl species for which Fermi resonance between 2ν₃ and ν₂ has been established.     

Acetylene spectra with a tunable diode laser: (ν4 + ν5)0+−ν41fQ branches of 12C2H2 and 12C13CH2

The rotational structure of the Q branches of the (ν₄ + ν₅)⁰⁺?ν₄^1f bands of ¹²C₂H₂ and ¹²C¹³CH₂ at 13.7 μm has been observed in a natural sample of acetylene by using a tunable diode laser as a source in a high-resolution infrared grating spectrometer equipped with a precision grating drive. Altogether 23 lines from J = 6 to 28 for ¹²C₂H₂ and 15 lines from J = 6 to 20 for ¹²C¹³CH₂ have been identified. The observed full width at half maximum of the resolved lines of these Q branches is very close to the calculated Doppler width. Molecular constants ν₀ + B″, B′ ? B″ ? 2D″, D′ ? D″, and H′ ? H″ have been derived from the measured line positions of the rotational structure.     

Correlations and accuracy of estimation of spectroscopic constants and term values

A comparison and evaluation of the various methods for reducing spectroscopic data to spectroscopic constants or term values is made with the aid of an analysis of a number of “synthetic” Σ-Σ bands generated from fixed sets of constants with random noise superimposed on the line positions. It is shown that the strong correlations that exist between the upper-state constants B′, D′ and the lower-state constants B₀, D₀ can be effectively broken up by using the difference constants ΔB = B′ - B₀ and ΔD = D′ - D₀, along with ν₀, for representing the upper states. The lower state constants B₀ and D₀ and their standard errors calculated from the combination differences Δ₂F″(J) are shown to be as good as those obtained from direct polynomial fits. If data for a number of bands originating in the same lower state are available, a considerable increase in accuracy of estimating the lower-state constants can be attained by analyzing the bands simultaneously, e.g., using combination differences, provided the data are free from systematic errors. The dependence of the accuracy of determining the constants B₀, D₀, ν₀, ΔB, and ΔD on the extent of the band analyzed was investigated by varying the minimum and maximum J-values. The plots showing this dependence for both the actual errors and standard errors can be used e.g., to assess the band size necessary to attain a desired accuracy for a given constant.Åslund's term-value method is cast in a form which permits simple derivation of explicit formulas for the correlation coefficients connecting all the upper- and lower-state term values, and of explicit relations between the term values and the combination differences. Modifications of the term-value method suitable for the case where one or more transitions originate in an unperturbed state are explored. It is shown that the “difference term values” referred to the lower (unperturbed) state with the same value of J, T_i(J)-T₀(J), are essentially uncorrelated to the lower state constants B₀ and D₀. Since these quantities can be expressed directly as the eigenvalues of the energy matrix for a given J in the presence of perturbations, their use for representing the energies of perturbed rovibronic states is recommended.     

Analysis of the 2ν3 band of 12CD3F at 5.06 μm recorded under high resolution

The 2ν₃(A₁) band of ¹²CD₃F near 5.06 μm has been recorded with a resolution of 20–24 × 10^?3 cm^?1. The value of the parameter (α^B ? α^A) for this band was found to be very small and, therefore, the K structure of the R(J) and P(J) manifolds was unresolved for J < 15 and only partially resolved for larger J values. The band was analyzed using standard techniques and values for the following constants determined: ν₀ = 1977.178(3) cm^?1, B″ = 0.68216(9) cm^?1, D″_J = 1.10(30) × 10^?6 cm^?1, α^B = (B″ ? B′) = 3.086(7) × 10^?3 cm^?1, and β^J = (D″_J ? D′_J) = ?3.24(11) × 10^?7 cm^?1. A value of α^A = (A″ ? A′) = 2.90(5) × 10^?3 cm^?1 has been obtained through band contour simulations of the R(J) and P(J) multiplets.     

Vibrational spectra and force constants of symmetric tops: Rotational analysis of ν3 and 2ν3 of H3Si35Cl and H3Si37Cl

The gas-phase infrared spectra of natural and ³⁵Cl isotopically enriched H₃SiCl have been recorded with a resolution of 0.04 cm^?1 in the regions of ν₃ (～550 cm^?1) and 2ν₃ (～1100 cm^?1). The fundamentals of species with ²⁸Si, ²⁹Si, ³⁰Si, ³⁵Cl, and ³⁷Cl and several hot bands of the series nν₃ + mν_i ? mν_i (n, m = 1, 2; i = 3 and 6) have been detected. The parameters ν₀, x₃₃, x₃₆, B₀, α₃^A, D_J⁰ and D_J³ were determined by a combination of least-squares analysis of P and R branches resolved into J peaks (J ≤ 90) and a band contour simulation. Possible resonances of nν₃ and (n ? 1)ν₃ + ν₆ are discussed.     

Vibrational spectra and force constants of symmetric tops: Rotational analysis of ν3 and several hot bands of H3SiI near 360 cm−1

The gas-phase infrared spectrum of natural H₃SiI has been recorded in the ν₃ range between 390 and 320 cm^?1 with a resolution of 0.04 cm^?1. The fundamental ν₃ and the three most intense “hot” bands 2ν₃ ? ν₃, 3ν₃ ? 2ν₃, and ν₃ + ν₆ ? ν₆ have been detected. The molecular parameters ν₀, x₃₃, x₃₆, B″, α₃^A, α₃^B, and D_J were determined by a least-squares analysis of the P and R branches resolved into J lines (J ≤ 110) and by a band contour simulation procedure, respectively.     

Vibrational spectra and force constants of symmetric tops: Rovibrational analysis of 2ν6 and 2ν6 − ν6 of H3Si35Cl and H3Si37Cl,and a new method for the determination of A0 and DK0

The gas-phase ir spectra of monoisotopic H₃Si³⁵Cl [35] and H₃Si³⁷Cl [37] in the 2ν₆ region near 1300 cm^?1 have been studied with a resolution of 0.05 cm^?1. A total of 467 and 1206 lines have been assigned for [35] and [37], respectively, and analyzed by a least-squares procedure, σ(J, K) ～ 6 × 10^?3cm^?1, to yield three parameters for the 2ν₆⁰ and six for the 2ν₆^±2 states for both isotopomers. In the ν₆ region $\text{32}\text{47}$ and $\text{127}\text{150}$ lines have been assigned to the hot bands 2ν₆⁰ ? ν₆^±1 and 2ν₆^±2 ? ν₆^±1 of [35] and [37], respectively. While a hot band 2ν_t⁰ ? ν_t^±1 does not provide any information above that available from ν_t^±1 and 2ν_t⁰, a hot band 2ν_t^±2 ? ν_t^±1 may supply extra data concerning the ground state. A new method for the evaluation of A₀ and D_K⁰ from combination differences of ν_t^±1, 2ν_t^±2, and 2ν_t^±2 ? ν_t^±1 of a symmetric top with C_3v symmetry is presented. Application to [35] and [37] yielded A₀ of 2.8447(5) and 2.8437(3) cm^?1, and D_K⁰ of 2.12(20) and 2.38(9) × 10^?5 cm^?1, respectively.     

High-resolution Fourier transform study of the perpendicular band ν11 of allene at 353 cm−1

The ν₁₁ perpendicular band of the allene (propadiene) molecule was measured in the region 310–390 cm^?1 on a high-resolution Fourier transform instrument. A total of 1880 lines was assigned to 22 subbands with KΔK values between ?10 and +12. Subband constants which reproduce the observed line positions with standard deviations of 0.0005-0.0008 cm^?1 are tabulated. The strong effects of the two types of l-type interactions allowed for this molecule are included in the Hamiltonian matrix used for the treatment of the spectrum and for the least-squares adjustment of the spectroscopic constants for the ν₁₁ state. A table of the rovibrational energy levels of the ν₁₁ state is given to facilitate analysis of the various hot bands observed throughout the spectrum of allene. Improved estimates are obtained for the elusive rotational constant, A₀, and for the centrifugal constant, D_K⁰, by combining published Raman data for the ν₁₁ band with the new accurate infrared measurements.     

High-resolution vibration-rotation spectroscopy of fluoroform-d

The vibration-rotation spectrum of the ν₂ and ν₅ fundamentals of CDF₃ have been recorded using a Nicolet 7199 Fourier transform infrared spectrometer; in addition the Q branch and several subbands of each of these transitions have been investigated using a tunable semiconductor diode laser spectrometer. The Q branch and the K structure in several P(J) and R(J) subbands of ν₂, and in several Q branches of ν₅, are resolved and assigned for the first time. Constants derived for these bands are (in cm^?1) ν₂ = 1111.1823₆, B₂ = 0.32928₂, A₂ = 0.18872₂, α₂^B = 16.44₅ × 10^?4, α₂^B ? α₂^A = 12.43₅ × 10^?4, D₀^j = 3.7₃ × 10^?7, D₂^J = 4.8₃ × 10^?7; ν₅ = 975.39₁, B₅ = 0.33062, A₅ = 0.18887, α₅^B = 2.83₁ × 10^?4, α₅^A = 2.4₃ × 10^?4, ζ₅ = 0.736, D₅^J ? D₀^J = 1.2₂ × 10^?8. Some of these constants are nearly 100 times more precise than those reported in previous work.     

Fourier transform infrared spectra of H2CS and D2CS

Infrared spectra of thoformaldehyde, H₂CS and D₂CS, were observed in the gas phase at a resolution of better than 0.1 cm^?1 from 4000 to 400 cm^?1 using a Nicolet FTIR system. Vibrational band origins and rotational constants were determined for ν₂, ν₃, ν₄, and ν₆ of H₂CS and for ν₁, ν₂, ν₃, ν₄, and ν₆ of D₂CS. The ν₃, ν₄, and ν₆ bands of H₂CS were analyzed as a set of three Coriolis interacting bands, and three Coriolis constants were determined; similarly the ν₄ and ν₆ bands of D₂CS were analyzed as a pair of interacting bands and one Coriolis constant was determined. A general harmonic force field was determined, without constraints, to fit the vibrational wavenumbers, Coriolis constants, and centrifugal distortion constants. A zero-point (r_z) structure was determined from the ground-state rotational constants, and the equilibrium (r_e) bond lengths were estimated.     

The high-resolution infrared spectrum of the ν11 band of allene-d4

The infrared band ν₁₁ around 300 cm^?1 of allene-d₄ has been studied at a resolution of 0.010 cm^?1. The J structure in the central Q branches of this perpendicular band was resolved and P- and R-lines were assigned to subbands with {K″} ≦ 18. A ground-state analysis resulted in B₀ = 0.232187(30) cm^?1, D₀^J = 6.3(1.0) × 10^?8cm^?1, and D₀^JK = 3.0(4) × 10^?6cm^?1. Upper-state constants including η₁₁^J and η₁₁^K were derived. Special attention was paid to the study of l-type doublings. Doublets due to q^(?)-doubling were resolved and accordingly the value q₁₁^(?) = ?0.000160(3) cm^?1 was derived. The more usual q⁽⁺⁾-doubling was also observed, and the result q₁₁⁽⁺⁾ = 0.000144(4) cm^?1 was obtained.