Far-infrared spectroscopy of CH3OD in highly excited torsional states and the atlas of the Fourier transform spectra in the range 200-350 cm(-1)

The high resolution Fourier transform far-infrared (FIR) spectrum of the torsion rotation band of CH3OD has been analyzed for the highly excited torsion states (n > or = 2) in the vibrational ground state. The spectrum shows splitting of the lines due to strong torsional-rotational-vibrational interactions in the molecule. Assignments were possible for rotational sub-bands in the torsional state as high as n = 4 and for K values up to 8 and J values of up to approximately 30 in most cases, for all the symmetry species. For the third excited torsional state n = 3 assignments were possible to K = 10. The data were analyzed with the help of the energy expansion model, which has been proven very successful in methanol. The state dependent expansion parameters are presented. These molecular parameters were able to reproduce the observed wavenumbers almost to within experimental accuracy of 0.0002 cm(-1) for clean unblended lines. These expansion coefficients should prove valuable in the calculation of precise energy values for excited torsional states up to n = 4, which is way above the torsional barrier. The detailed high-resolution spectral atlas of CH3OD has been presented in the range 200-350 cm(-1). This atlas is an extension of our earlier atlas in the range 20-205 cm(-1). The availability of this atlas in the journal will be very valuable for spectroscopists and astrophysicists seeking information in the infrared (IR) region in the laboratory and in outer space.     

The Bending Vibrational Ladder of HCN by Hot Gas Emission Spectroscopy

High-resolution measurements have been made on the infrared emission spectrum of the doubly substituted HCN isotopomer, H¹³C¹⁵N, at temperatures on the order of 1370 K. The measurements cover the region 400-850 cm⁻¹ with a resolution (1/MOPD) of 0.006 cm⁻¹. We could assign hot bands with upper levels up to the 0 11¹¹ 0 state. The assignments have been verified for states up to v₂=5 by fitting with earlier room temperature absorption measurements of overtone and hot bands. All the measurements for H¹³C¹⁵N have been combined in a single least-squares fit that includes approximately 8670 rovibrational lines which have a root-mean-square deviation on the order of 0.000 33 cm⁻¹. The spectroscopic constants for the bending states v₂=1,…,11 are reported, as well as those for some combination states involving the two stretching modes.     

High-Temperature Infrared Emission Measurements on HNC

The emission spectrum of HNC has been measured from 400 to 4100 cm(-1). The HNC was observed as an equilibrium mixture of HCN and HNC in a fused quartz cell heated to 1370 K. The three fundamental bands and many hot bands of HNC were measured with resolutions ranging from 0.006 cm(-1) for the lowest fundamental to 0.033 cm(-1) for the other two. High rotational levels up to J=62 were observed as well as vibrational levels up to v(2)=5. Now all the quadratic contributions to the vibrational and rotational term values have been determined, as well as some higher order terms. Copyright 2001 Academic Press.     

Complete experimental rovibrational eigenenergies of HNC up to 3743 cm(-1) above the ground state

The [H,C,N] system is one of the ideal candidate molecules to test new models aimed to calculate the manifold of the rotational, vibrational, and electronic states of a triatomic molecule. The isomerization reaction HCN?HNC is one of the most important model systems for the study of unimolecular reactions. This paper reports on the experimental characterization of all 1191 eigenenergies up to 3743 cm(-1) relative to the ground state in the HNC part of the potential surface using high temperature hot gas emission spectroscopy. The spectroscopic constants for the first 27 vibrational states including highly excited bending vibrations up to v(2) = 7 are reported. The first 14 rotational perturbations have been identified and the perturbed eigenenergies were determined. The 3200 eigenenergies up to J = 70 for the first 47 vibrational substates are included as supplement to this paper.     

New Analysis of the ν3 fundamental band of HDCO: Positions and intensities

Using high-resolution Fourier transform spectra of mono deuterated formaldehyde (HDCO) recorded in the 5.8-μm spectral range at Giessen (Germany), we carried out an extensive analysis of the strong ν₃ fundamental band (carbonyl stretching mode) at 1724.2676 cm⁻¹, starting from results of a previous analysis [J.W.C. Johns, A.R.W. McKellar, J. Mol. Spectrosc. 64 (1977) 327-339]. For this hybrid band (with both A- and B-type transitions) the analysis was pursued up to high rotational quantum numbers. In this way, it was possible to evidence a resonance which perturbs the ν₃ lines for high K_a values which is due to the existence of the 2ν₅ and ν₅ + ν₆ dark bands in the same spectral region. In addition a local resonance is perturbing the 3¹ levels in  = 8 which is due to a crossing with the 4¹ energy levels in K_a = 11. The model used to calculate the energy levels accounts for the observed A- type, B- type C-type Coriolis (and/or) Fermi resonances which couple the 3¹ and the 5¹6¹, 5², and 4¹ energy levels. However the 4¹ state is also involved in strong vibration-rotation interactions coupling the {5¹,6¹,4¹} system of resonation states of HDCO [A. Perrin, J.M. Flaud, L. Margulès, J. Demaison, H. Mäder, S. Wörmke, J. Mol. Spectrosc. 216 (2002) 214-224]. Therefore the final energy levels calculation was performed for the {5¹,6¹,4¹,3¹,5²,5¹6¹} resonating states and in this way it was possible to reproduce the observed line positions, within their experimental uncertainties. The present work also led to the determination of the intensity ratio of the B- to A-type components of the ν₃ band I_A/I_B ∼24 band from spectral fittings performed in several parts of the observed spectrum. Finally, using the 5.8 μm band intensity available in the literature we generated, for the first time, a list of line parameters (positions and intensities) for the 5.8 μm region of HDCO.     

Infrared Transitions of HCN and HCN between 500 and 10 000 cm

We have measured the Fourier transform spectrum (FTS) of two isotopomers of hydrogen cyanide (H¹²C¹⁴N and H¹²C¹⁵N) from 500 to 10 000 cm⁻¹. The infrared data have been combined with earlier published microwave and submillimeter-wave measurements. From this analysis new vibration–rotation energy levels and constants are given, based on the observation of a number of new vibrational levels, especially for H¹²C¹⁵N. The Coriolis interaction involving Δv₃= −1, Δv₂= 3, and Δl= ±1 has been observed for a great many levels and in some cases the assignments of laser transitions allowed by this interaction are more clearly shown. New vibration–rotation constants are given that allow one to predict the transition wavenumbers for most of the transitions below 10 000 cm⁻¹with accuracies of about 0.5 cm⁻¹or better. Values are given for the power series expansion of thel-type resonance constants and for the centrifugal distortion constants, as well as the usual vibrational and rotational constants.     

Complete experimental rovibrational eigenenergies of HCN up to 6880 cm(-1) above the ground state

The [H,C,N] molecular system is a very important model system to many fields of chemical physics and the experimental characterization of highly excited vibrational states of this molecular system is of special interest. This paper reports the experimental characterization of all 3822 eigenenergies up to 6880 cm(-1) relative to the ground state in the HCN part of the potential surface using high temperature hot gas emission spectroscopy. The spectroscopic constants for the first 71 vibrational states including highly excited bending vibrations up to v(2) = 10 are reported. The perturbed eigenenergies for all 20 rotational perturbations in the reported eigenenergy range have been determined. The 11,070 eigenenergies up to J = 90 for the first 123 vibrational substates are included as supplement to this paper. We show that a complete ab initio rovibrational analysis for a polyatomic molecule is possible. Using such an analysis we can understand the molecular physics behind the Schro?dinger equation for problems for which perturbation theoretical calculations are no more valid. We show that the vibrational structure of the linear HCN molecule persists approximately up to the isomerization barrier and only above the barrier the accommodation of the vibrational states to the double well structure of the potential takes place.     

Rovibrational eigenenergy structure of the [H,C,N] molecular system

The vibrational-rotational eigenenergy structure of the [H,N,C] molecular system is one of the key features needed for a quantum mechanical understanding of the HCN?HNC model reaction. The rotationless vibrational structure corresponding to the multidimensional double well potential energy surface is well established. The rotational structure of the bending vibrational states up to the isomerisation barrier is still unknown. In this work the structure of the rotational states for low and high vibrational angular momentum is described from the ground state up to the isomerisation barrier using hot gas molecular high resolution spectroscopy and rotationally assigned ab initio rovibronic states. For low vibrational angular momentum the rotational structure of the bending excitations splits in three regions. For J < 40 the structure corresponds to that of a typical linear molecule, for 40 < J < 60 has an approximate double degenerate structure and for J > 60 the splitting of the e and f components begins to decrease and the rotational constant increases. For states with high angular momentum, the rotational structure evolves into a limiting structure for v(2) > 7--the molecule is locked to the molecular axis. For states with v(2) > 11 the rotational structure already begins to accommodate to the lower rotational constants of the isomerisation states. The vibrational energy begins to accommodate to the levels above the barrier only at high vibrational excitations of v(2) > 22 just above the barrier whereas this work shows that the rotational structure is much more sensitive to the double well structure of the potential energy surface. The rotational structure already experiences the influence of the barrier at much lower energies than the vibrational one.     

Near infrared emission spectrum of HCN

To record the infrared emission of hot molecular gases an optimized emission apparatus for the Bruker IFS 120 HR high-resolution FT-IR spectrometer has been constructed. Using this apparatus the hot gas emission spectrum of HCN at 1420 K has been recorded in the wavenumber region of 6000-6800 cm⁻¹ with a resolution of 0.044 cm⁻¹. This work reports the analysis of 33 bands with 58 subbands (9200 line positions). Thirty-seven rovibronic states of HCN including at 12 603 cm⁻¹ have been characterized for the first time and for 25 other states it was possible to improve the existing spectroscopic constants substantially. The very dense emission spectrum with many overlapping features was analyzed with new spectrum analysis software implemented using the Mathematica^TM computer algebra system. Spectroscopic constants have now been determined for 220 HCN rovibronic states. For 102 states the rovibrational spectroscopic constants have been determined for the first time or improved substantially using emission spectra measured in Giessen.     

Analysis of the first triad of interacting states (0 2 0), (1 0 0), and (0 0 1) of D2O from hot emission spectra

The far-infrared and middle-infrared emission spectra of deuterated water vapour were measured at temperatures 1370, 1520, and 1940 K in the ranges 320-860 and 1750-3400 cm⁻¹. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. More than 3550 new measured lines for the D₂¹⁶O molecule corresponding to transitions from highly excited rotational levels of the (0 2 0), (1 0 0), and (0 0 1) vibrational states are reported. These new lines correspond to rotational states with higher values of the rotational quantum numbers compared to previously published determinations: J_max = 29 and K_a(max) = 22 for the (0 2 0) state, J_max = 29 and K_a(max) = 25 for the (1 0 0) state, and J_max = 30 and K_a(max) = 23 for the (0 0 1) state. The extended set of 1987 experimental rotational energy levels for the (0 2 0), (1 0 0), and (0 0 1) vibration states including all previously available data has been determined. For the data reduction we used the generating function model. The root mean square (RMS) deviation between observed and calculated values is 0.004 cm⁻¹ for 1952 rovibrational levels of all three vibration states. A comparison of the observed energy levels with the best available values from the literature and with the global predictions from molecular electronic potential energy surfaces of water isotopic species [H. Partridge, D.W. Schwenke, J. Chem. Phys. 106 (1997) 4618] is discussed. The latter confirms a good consistency of mass-dependent DBOC corrections in the PS potential function with new experimental rovibrational data.