The infrared spectrum of fulminic acid,HCNO, in the ν4 fundamental region

The infrared spectrum of fulminic acid, HCNO, was measured with high resolution in the region 500–657 cm^?1. The spectrum was obtained with a Bomem interferometer, at a reslution of about 0.006 cm^?1. Thirteen bands could be identified and assigned to rovibrational transitions of HCNO. These are the fundamental ν₄ and some of its hot bands, and the overtone 2ν₅ and some of its hot bands. Because ν₅ is a quasilinear bending mode, the identification and measurement of the various hot bands is especially important for locating the combination states of ν₄ with various quanta of ν₅.     

Vibration-rotation interaction in HCNO caused by accidental resonances and enhanced by the quasilinearity of the molecule

The recent assignment of the vibrational spectrum of the quasilinear molecule HCNO revealed several near coincidences between vibrational energy levels involving the two bending modes, ν₄ (skeletal bending mode) and ν₅ (HCN-bending mode), and the lowest-lying stretching mode, ν₃ (NO stretching mode). By considering the correlation between the energy levels of a linear and a bent molecular model of HCNO, it is seen that resonance interactions which would be of third or higher order in a linear molecule Hamiltonian would be of first or second order in the Hamiltonian of a bent molecule, and thus might be significant in the quasilinear molecule HCNO. In this way we were able to identify the type of observed interaction occurring between three pairs of nearly coincident levels, (00010, 00002), (00020, 00012), and (00100, 00004). Anomalous centrifugal distortion effects had been observed and reported earlier for the pure rotational transitions arising from molecules in the 00010, 00020, and 00002 levels. Rotational transitions arising from molecules in the 00004 and 00100 vibrational states of HCNO and the 00100 state of DCNO are reported here for the first time. For two pairs of levels, (00010, 00002) and (00100, 00004), we could determine the magnitude of the coefficients of the interaction matrix elements from an analysis of the centrifugal distortion effects.     

High-resolution Q-branches spectrum of C2H2 at 9366 and 9407 cm−1

The acetylene absorption spectrum in the Nd-laser range 9240–9520 cm^?1 has been recorded earlier (1), using a highly sensitive intracavity laser spectrometer. Two weak absorption perpendicular bands 2100⁰1¹ ← 0000⁰0⁰ (ν₀ = 9366.6 cm^?1) and 1200°3¹ ← 0000°0° (ν₀ = 9407.7 cm^?1) were studied and spectroscopic constants were obtained. However, the structure of the Q branches of these bands with J < 7 was unresolved because the resolution of the spectrometer was not very high.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.     

Matrix isolation studies and potential function for perfluorocyclobutane

The infrared and Raman spectra of perfluorocyclobutane isolated in argon matrices at 1:100 and 1:200 mole ratios have been measured between 200 and 2000 cm^?1. Although the ring-puckering fundamental (ν₁₆) was not observed directly, an assignment for the 2 ← 1 (30 cm^?1) transition of ν₁₆ has been deduced from sum and difference bands resolved in the infrared spectrum. Potential functions based upon valence force models are considered in detail and correlated with those of similar ring systems. By using the frequency of the 2 ← 1 transition for ν₁₆ and a vibrational reduced mass of 1501 amu, an approximate model potential function calculation yields a slightly puckered equilibrium conformation with a barrier on the order of 124 cm^?1. The vibrational assignment for perfluorocyclobutane is discussed in terms of the new matrix isolation spectra.     

The two-dimensional anharmonic oscillator: Vibration-rotation constants of fulminic acid,HCNO

The lowest-wavenumber vibration of HCNO and DCNO, ν₅, is known to involve a largeamplitude low-frequency anharmonic bending of the CH bond against the CNO frame. In this paper the anomalous vibrational dependence of the observed rotational constants B(v₅, l₅), and of the observed l-doubling interactions, is interpreted according to a simple effective vibration-rotation Hamiltonian in which the appropriate vibrational operators are averaged in an anharmonic potential surface over the normal coordinates (Q_5x, Q_5y). All of the data on both isotopes are interpreted according to a single potential surface having a minimum energy at a slightly bent configuration of the HCN angle (～170°) with a maximum at the linear configuration about 2 cm^?1 higher. The other coefficients in the Hamiltonian are also interpreted in terms of the structure and the harmonic and anharmonic force fields; the substitution structure at the “hypothetical linear configuration” determined in this way gives a CH bond length of 1.060 Å, in contrast to the value 1.027 Å determined from the ground-state rotational constants.We also discuss the difficulties in rationalizing our effective Hamiltonian in terms of more fundamental theory, as well as the success and limitations of its use in practice.     

Carbon suboxide: The infrared spectrum from 1800 to 2600 cm−1

The infrared spectrum of carbon suboxide has been recorded from 1800 to 2600 cm^?1 at a resolution of 0.003 cm^?1. About 7% of the ca. 40 000 lines observed have been assigned and analyzed, belonging to 36 different bands. Most of these are associated with the fundamental ν₃, at 2289.80 cm^?1, and the combination band ν₂ + ν₄, at 2386.61 cm^?1, each of which give rise to a system of sum bands, difference bands, and hot bands involving the low-wave-number fundamental ν₇ at 18 cm^?1. A few other tentative assignments are made. The bands have been analyzed for vibrational and rotational constants.     

The ν4 and ν2 Raman bands of CHD3

The CHD₃ Raman spectrum from 1925 to 2455 cm^?1 has been photographed with a resolution of about 0.2 cm^?1, showing the overlapping ν₂ and ν₄ bands. Ground state combination differences yield C₀ = 2.6297 ± 0.0003 cm^?1. The ν₄ state is weakly perturbed, but reasonably accurate values could be obtained for ν₄ = 2250.88 ± 0.10 cm^?1, (Cζ)₄ = 0.656 ± 0.010 cm^?1, C₄ - C₀ and B₄ - B₀. Some of these constants differ significantly from values previously estimated by infrared workers. For the ν₂ state the constants determined are in good agreement with recent infrared results.     

A reevaluation of the assignment of the vibrational fundamentals and the rotational analysis of bands in the high-resolution infrared spectra of trans- and cis-1,3,5-hexatriene

Assignments of the vibrational fundamentals of cis- and trans-1,3,5-hexatriene are reevaluated with new infrared and Raman spectra and with quantum chemical predictions of intensities and anharmonic frequencies. The rotational structure is analyzed in the high-resolution (0.0013-0.0018 cm⁻¹) infrared spectra of three C-type bands of the trans isomer and two C-type bands of the cis isomer. The bands for the trans isomer are at 1010.96 cm⁻¹ (ν₁₄), 900.908 cm⁻¹ (ν₁₆), and 683.46 cm⁻¹ (ν₁₇). Ground state (GS) rotational constants have been fitted to the combined ground state combination differences (GSCDs) for the three bands of the trans isomer. The bands for the cis isomer are at 907.70 cm⁻¹ (ν₃₃) and 587.89 cm⁻¹ (ν₃₅). GS rotational constants have been fitted to the combined GSCDs for the two bands of the cis isomer and compared with those obtained from microwave spectroscopy. Small inertial defects in the GSs confirm that both molecules are planar. Upper state rotational constants were fitted for all five bands.     

High resolution infrared spectrum of the ν4 band of DCCF

The bending vibration-rotation band ν₄ of DCCF was studied. The measurements were carried out with a Fourier spectrometer at a resolution of about 0.03 cm^?1. The constants B₀=0.29141(1)cm^?1, α₄=?5.02(2)×10^?4cm^?1, q₄=4.52(3)×10^?4cm^?1, and D₀=9.2(4)×10^?8cm^?1 were derived. The rotational analysis of the “hot” bands 2ν₄(Δ) ← ν₄(II) and 2ν₄(Σ⁺) ← ν₄(II) was performed. In addition, the “hot” bands ν₄ + ν₅ ← ν₅ were assigned. A set of vibrational constants involved was derived.     

High resolution Fourier transform infrared spectra and analysis of the ν14, ν15 and ν16 bands of azetidine

Rotationally resolved vibrational spectra of the three lowest frequency bands of the four-membered heterocycle azetidine (c-C₃H₆NH) have been collected with a resolution of 0.00096 cm⁻¹ using the far infrared beamline at the Canadian Light Source synchrotron. The modes observed correspond principally to motions best described as: β-CH₂ rock (ν₁₄) at 736.701310(7) cm⁻¹, ring deformation (ν₁₅) at 648.116041(8) cm⁻¹, and the ring puckering mode (ν₁₆) at 207.727053(9) cm⁻¹. A global fit of 14 276 rovibrational transitions from the three bands provided an accurate set of ground state spectroscopic constants as well as excited state parameters for each of the three vibrational modes. The ground state structure was determined to be that of the puckered conformer having the NH bond in an equatorial arrangement.     

High-resolution infrared spectrum of carbon suboxide: The ν4 + 2ν70 and ν4 + 3ν71 − ν71 bands

The infrared spectrum of the ν₄ + 2ν₇ progression of C₃O₂ has been recorded with a resolution of about 0.018 cm^?1. Two bands of the progression have been completely analyzed. The band centers obtained in this study establish, when combined with previously published experimental results, than 3ν₇¹ is 97.22 cm^?1 above the ground vibrational state.     

A high-resolution study of the ν7 band of propyne

The infrared spectrum of propyne (methyl acetylene) between 1300 and 1620 cm^?1 has been reanalyzed at a resolution of 0.006 cm^?1. The main Fermi and Coriolis interactions of the ν₇^±1 band have been identified, as has the Fermi interaction between (ν₈ + ν₁₀)⁰ and ν₄⁰. Reassignment of a subband shows that ν₄⁰ has a very small transition moment. Thirty-eight molecular parameters for the interacting excited vibrational levels were determined by a least-squares analysis of 1550 lines.     

High-resolution rovibrational analysis of vibrational states of A2 symmetry of the dideuterated methane CH2D2: the levels ν 5 and ν 7 + ν 9

The infrared spectrum of the CH₂D₂ molecule has been measured in the region 900–1500?cm^?1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.0024?cm^?1 (FWHM, unapodized). Transitions belonging to the hot bands ν ₇?+?ν₉?ν ₇, ν₇?+?ν₉? ν ₉, ν₅?+?ν₇?ν₅, and ν₅?+?ν₉?ν₅ were extracted from the recorded spectra to determine the rovibrational energies of the A₂ symmetry vibrational states (v ₇?=?v ₉?=?1) at 2329.698?cm^?1 and (v ₅ ?=?1) at 1331.409?cm^?1. Vibrational energies as well as rotational and centrifugal distortion parameters of the (v ₇?=?v ₉=1) and (v ₅?=?1) states were determined that reproduce the experimental rovibrational energy levels of the (v ₇?=?v ₉?=?1) and (v ₅?=?1) vibrational states with a d _rms deviation of 0.0017 and 0.0006?cm^?1, respectively. The results are discussed in relation to the equilibrium structure of methane, which is redetermined here from the experimental data, and in relation to its potential hypersurface and anharmonic vibrational dynamics.     

The bending vibration bands ν4 and ν5 of HCCI

The bending vibration bands ν₄ and ν₅ of HCCI were studied. From the observed rotational structure the rotational constant B₀ and the centrifugal distortion constant D₀ were obtained. The results were B₀ = 0.105968(7) cm^?1 and D₀ = 1.96(7) × 10^?8 cm^?1 from ν₄ and B₀ = 0.105948(8) cm^?1 and D₀ = 1.96(11) × 10^?8 cm^?1 from ν₅. The structure of the hot bands 2ν₅(Δ) ← ν₅(Π) and 3ν₅(φ) ← 2ν₅(Δ) was also resolved and hence the values α₅ = ?3.033(8) × 10^?4 cm^?1 and q₅ = 9.3(3) × 10^?5 cm^?1 could be derived. The other most intense hot bands following ν₅ could be explained in terms of the Fermi diads $\text{ν}{}_3\text{2ν}{}_5{}^0$ and $\text{ν}{}_3\text{+}\text{ν}{}_5{}^{\mathrm{\pm 1}}\text{3ν}{}_5{}^{\mathrm{\pm 1}}$. Of the numerous hot bands accompanying ν₄, only those between different excited states of ν₄ could be assigned. Then estimates for α₄ and q₄ were also obtained. In addition, several vibrational constants were derived.     

The high-resolution infrared spectrum of pyrrole between 900 and 1500 cm revisited

The Fourier transform gas-phase infrared spectrum of pyrrole, C₄H₅N, has been recorded with a resolution of ca. 0.003 cm⁻¹ in the 900-1500 cm⁻¹ spectral region. Four fundamental bands, ν₈(A₁; 1016.9 cm⁻¹), ν₂₃(B₂; 1049.1 cm⁻¹), ν₇(A₁; 1074.6 cm⁻¹), ν₂₀(B₂; 1424.4 cm⁻¹) and the overtone band 2ν₁₆(A₁; 962.7 cm⁻¹) have been analysed using the Watson model. The ν₈ and 2ν₁₆ bands are unperturbed; the ν₇ and ν₂₃ bands are locally perturbed, while the ν₂₀ band is globally perturbed by weak c-Coriolis resonance. Upper state vibrational term values, and rotational and centrifugal distortion constants, have been obtained from fits using S-reduction and I^r-representation as well as A-reduction and III^r-representation. A set of ground state rotational and centrifugal distortion constants using A-reduction was obtained from a simultaneous fit of ground state combination differences from all five bands and previous microwave and millimetre-wave data.     

High resolution infrared synchrotron study of CH2D81Br: ground state constants and analysis of the ν5, ν6 and ν9 fundamentals

The high resolution infrared absorption spectrum of CH₂D⁸¹Br has been recorded by Fourier transform spectroscopy in the range 550–1075?cm^?1, with an unapodized resolution of 0.0025?cm^?1, employing a synchrotron radiation source. This spectral region is characterized by the ν₆ (593.872?cm^?1), ν₅ (768.710?cm^?1) and ν₉ (930.295?cm^?1) fundamental bands. The ground state constants up to sextic centrifugal distortion terms have been obtained for the first time by ground-state combination differences from the three bands and subsequently employed for the evaluation of the excited state parameters. Watson's A-reduced Hamiltonian in the I^r representation has been used in the calculations. The ν ₆?=?1 level is essentially free from perturbation whereas the ν ₅?=?1 and ν ₉?=?1 states are mutually interacting through a-type Coriolis coupling. Accurate spectroscopic parameters of the three excited vibrational states and a high-order coupling constant which takes into account the interaction between ν₅ and ν₉ have been determined.     

The infrared spectrum of C2N2 in the region of the bending fundamental ν5

The high resolution infrared spectrum of C₂N₂ in the region 200–270 cm^?1 has been studied with a Fourier transform spectrometer. In addition to ν₅, the “hot” bands 2ν₅⁰ ← ν₅¹, 2ν₅² ← ν₅¹ and 3ν₅³ ← 2ν₅² have been analysed. Polynomial fits have been applied to obtain the vibrational term values and the rotational constants for the levels involved.     

First analysis of the 3ν9−ν9 hot band of difluoroboric acid (BF2OH). Further evidence of large amplitude effects for the OH torsion

The hot band 3ν₉?ν₉ of the isotopologue ¹¹BF₂OH (difluoroboric acid) located at 1034.78 cm^?1 was investigated for the first time by Fourier transform infrared spectroscopy. During previous studies both, the ν₉ mode (OH-torsion relative to the BF₂ moiety, at 522.87 cm^?1) and the ν₄ mode (in-plane OH bend) had been shown to exert large amplitude motion, and splittings of 0.0051 and 0.0038 cm^?1 had been observed in the interacting 2ν₉ and ν₄ bands located at 1042.87 and 961.49 cm^?1, respectively. The present work establishes large amplitude effects also for the 9³ excited state located at 1557.655 cm^?1. Numerous P and R transitions of the 3ν₉–ν₉ hot band were identified in the 2ν₉ manifold, and doublets corresponding to a torsional splitting of 0.031 cm^?1 in the 9³ state were observed. The vibrational assignment of the 9³ state was confirmed by the detection of the 3ν₉?2ν₉ hot band Q branch in the 19 μm region.     

The infrared spectrum of 13C2HD between 100 and 2100 cm−1: a global fit for the bending states up to υ 4 + υ 5 = 3

The fundamental bending ro-vibrational bands and a number of overtone, combination and hot bands of ¹³C₂HD have been recorded by Fourier transform infrared spectroscopy in the range 450–2100 cm^?1. In addition, the ν ₅ ← ν ₄ band, centred at 164.65 cm^?1, has been identified in the spectrum of ¹³C₂H₂. The data were analysed simultaneously in a global fit that has provided very accurate rotational and vibrational parameters for the ground and vibrationally excited states.