Rovibrational and Rotational Spectroscopy of Levels of Propyne around 1000 cm(-1).

Four vibrational levels in the energy region around 1000 cm(-1) were studied. These were the v(5)=1 and v(8)=1 fundamental levels, both components of the v(9)=v(10)=1 combination level (l(9)=l(10)=+/-1 and l(9)=-l(10)=+/-1), and both components of the v(10)=3 overtone level (l(10)=+/-1 and +/-3). New FTIR spectra with a synchrotron radiation source were recorded in the region of the "superhot" v(10)=3<--2 bands, which made possible the first assignment of levels of the v(10)=3(+/-1) sublevel. More than 330 new rotational transitions in the combination and overtone levels were measured by millimeter-wave spectroscopy betwen 50 and 360 GHz. The new data were analyzed simultaneously together with the previously assigned rovibrational data for the fundamental and combination levels and rotational data for the fundamental levels using a global model with all anharmonic, Coriolis, l-type, and alpha-resonances. Significant improvement of data reproduction and very good consistency with the Hamiltonian parameters of the lower vibrational levels v(9)=1 and v(10)=1, 2 were achieved. A strong dependence of the A(v) constant on the l(10) quantum number is found for propyne: this is shown to be characteristic of skeleton C-C identical withC or C-C identical withN bending modes in H(3)CCCH, H(3)CCN, and their fully deuterated species. Copyright 2001 Academic Press.

The Ground and First Excited Torsional States of Acetic Acid.

A global fit of microwave and millimeter-wave rotational transitions in the ground and first excited torsional states (v(t) = 0 and 1) of acetic acid (CH(3)COOH) is reported, which combines older measurements from the literature with new measurements from Kharkov, Lille, and NIST. The fit uses a model developed initially for acetaldehyde and methanol-type internal rotor molecules. It requires 34 parameters to achieve a unitless weighted standard deviation of 0.84 for a total of 2518 data and includes A- and E-species transitions with J

High-Resolution Infrared and Millimeter-Wave Study of the Fermi-Coupled v(2) = 1 and v(3) = 2 States of DSiF(3).

The nu(2) (nu(eff.) 854.841 cm(-1)) and 2nu(3) infrared bands (nu(eff.) 840.083 cm(-1)) of DSiF(3) have been studied with a resolution of 2.5 x 10(-3) cm(-1). Moreover, millimeter-wave transitions in the v(2) = 1 and v(3) = 2 states up to J" = 33 have been measured. The assignments and fit of the poorly resolved, compressed cluster-type 2nu(3) IR transitions have been confirmed by a simultaneous study of the 2nu(3)-nu(3) band. The constant W = 5.116 cm(-1) of the Fermi interaction between the v(2) = 1 and v(3) = 2 levels has been determined from frequency effects which are in agreement with relative intensities of the nu(2) and 2nu(3) bands. The deperturbed (B(0) - B(v)) and (C(0) - C(v)) values of the states involved agree with their ab initio predictions within 7% in the worst case. Copyright 2001 Academic Press.

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.

Radiofrequency, Centimeter-Wave, Millimeter-Wave, and Infrared Spectra of SiHF(3): Investigation of the Ground, v(4) = 1, and v(6) = 1 Vibrational States.

The present paper deals with the analysis of the microwave, millimeter-wave, and infrared spectra of (28)SiHF(3) in its ground, v(6) = 1 and v(4) = 1 excited states. The former was observed up to 1055 GHz leading to the determination of one octic centrifugal distortion constant, L(J) = -0.0749(55) µHz. Furthermore the interaction term ||h(3,GS) || = 1.1032(70) mHz has been fitted from splittings of six K = 3 lines. The excited states have been regarded as isolated ones. This enabled fits according the Q-, D-, and QD-reduction schemes proposed by E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev, (J. Mol. Spectrosc. 126, 159-170 (1987)) and further developed by J. K. G. Watson, C. Gerke, H. Harder, and K. Sarka, (J. Mol. Spectrosc. 187, 131-141 (1997)) and Harder (J. Mol. Spectrosc. 194, 145 (1999)). A multiple fit analysis was performed confirming the assumption that the excited states are not affected by intervibrational resonances. Finally the millimeter spectrum of (29)SiHF(3) and (30)SiHF(3) in their ground state was also measured up to 460 GHz and accurate rotational and centrifugal distortion parameters were derived. Copyright 2000 Academic Press.

Analysis of Rotational and Rovibrational Spectra of SiDF(3) in the Ground and v(4) = 1 Excited States.

This paper presents the analysis of the spectra of SiDF(3) in its vibrational ground and v(4) = 1 states. The pure rotational spectrum of the ground state was measured up to 903 GHz (J" = 65). Rotational, quartic, and sextic centrifugal distortion constants were accurately determined. Furthermore the parameter ||h(3) || = 7.64(11) x 10(-4) Hz was derived from the observation of A(1)-A(2) splittings of six K = 3 lines. The assignment of the v(4) = 1 spectrum was performed by combining 140 pure rotational frequencies and more than 2300 rovibrational transitions. Among them, because of the strong (+/-2, -/+4) interaction, there are more than 90 A(1)-A(2) resolved split transitions between the (l = 0, k = +/-3) ground state levels and the (l = +/-2, k = -/+1) v(4) = 1 levels. Although the v(4) band is located at about 994.3 cm(-1), the energies of the other fundamental bands are at a distance of more than 140 cm(-1). The assumption of the isolated character of the state was confirmed by the small differences between the v(4) = 1 state and the ground state parameters and by the possibility of using the D and Q reduction schemes proposed by E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev [J. Mol. Spectrosc. 126, 159-170 (1987)]. Copyright 1999 Academic Press.

Mid- and Near-Infrared Spectra, Millimeterwave Spectra, and Global Analysis of (16)O(12)C(80)Se.

We have recorded a total of 12 FTIR spectra of monoisotopic OC(80)Se in different spectral regions with a resolution (1/maximum optical path difference) between 2.7 and 13.2 x 10(-3) cm(-1). These spectra spanned the range from 350 to 7800 cm(-1), many bands being studied with different p x L products in order to also detect weak hot bands. Altogether 18 band systems comprising 81 different bands, mostly of Sigma type, were observed and analyzed by means of polynomial expansions in J(J + 1). New rotational transitions of vibrationally excited states as high as 2200 cm(-1) with J" 17-25 in the 140-210 GHz and J" 53-58 in the 430-470 GHz millimeterwave regions were measured with the assistance of predictions by the global fit. This fit was performed using a weighted least-squares procedure and employing the whole body of data, and about 100 molecular parameters were determined that describe the energy level of (16)O(12)C(80)Se with statistical accuracy. Improved highly accurate ground state parameters up to sextic centrifugal distortion terms were obtained by a merge of ground state combination differences and pure rotational data. The v(1), v(2), v(3) polyad interacts anharmonically with the v(1) - 1, v(2) + p, v(3) + q polyads with p + 2q = 4. Moreover, some local crossings with Coriolis interactions between (v(1), v(2), v(3)) and (v(1) - 1, v(2) + 3, v(3) + 1) levels were observed and treated perturbationally. Copyright 1999 Academic Press.

Radio-Frequency, Centimeter-Wave, Millimeter-Wave, and Infrared Spectra of SiDF(3) in the v(6) = 1 Excited State.

This paper deals with the first study of high-resolution radio-frequency, centimeter-wave, millimeter-wave, and infrared spectra of the deuterated isotopomer of trifluorosilane, SiDF(3), in its lowest degenerate excited v(6) = 1 state. Following the work of E. I. Lobodenko, O. N. Sulakshina, V. I. Perevalov, and Vl. G. Tyuterev, (J. Mol. Spectrosc. 126, 159-170 (1987)) and Harder (J. Mol. Spectrosc. 194, 145 (1999)), the data (18 A(1)-A(2) transitions, 229 l-type resonance transitions, 189 pure rotational transitions, and 1167 rovibrational transitions) have been fitted using three equivalent Q, D, and QD reduction schemes enabling the fit of one of the three interaction parameters d, q(12), and epsilon, respectively, while the other two are fixed to zero. In addition to further higher order constants, either f(K)(22) or tau(K) also had to be constrained. By checking the standard deviation of each data set and the relations between parameters determined within different constrains, the six reduction schemes have been shown to be unitary equivalent. Furthermore, the axial rotational ground state constant C(0) has been accurately determined. Copyright 1999 Academic Press.

The Ground State Rotational Spectra of HDCO and D2CO.

The ground state rotational spectra of HDCO and D2CO have been measured from 5 to 2000 GHz. These new measurements together with older ones have been fitted to a standard A-reduced Watson-type Hamiltonian. The accuracy of the rotational and centrifugal distortion constants has been significantly improved. It has to be noted that it was necessary to include octic constants. The experimental constants are compared to ab initio predictions. Copyright 1999 Academic Press.

Analysis of the Rotational Spectra of SiH3CN and Its Isotopomers: Experimental and Ab Initio Determinations of the Dipole Moment and the Structure.

The ground state rotational spectra of SiH3CN and its 29Si, 30Si, 13C, 15N, d1, d2, and d3 isotopic species have been measured by Fourier transform microwave spectroscopy and by millimeterwave spectroscopy. Accurate rotational, centrifugal distortion, and 14N and D nuclear quadrupole coupling constants have been derived. The dipole moment of the parent species has also been measured, µ = 3.4400(42) D. The structure, force field, dipole moment, and nuclear quadrupole coupling constants have been calculated ab initio at the SCF, MP2, and B3LYP levels using triple zeta polarized basis sets. The experimental ro, rs, and rz structures have been determined. An approximate equilibrium structure has been obtained by combining the experimental results and the ab initio calculations: re(C&tbond;N) = 1.159 Å, re(Si&sbond;C) = 1.848 Å, re(Si&sbond;H) = 1.470 Å, and angle(HSiC) = 107.4 degrees. Copyright 1998 Academic Press.

High-Resolution Infrared Spectrum of D3Si79Br in the nu1/nu4 Region: The Structure of Silyl Bromide

FTIR spectra of monoisotopic D3Si79Br covering the bands nu1 (a1, 1580.637 cm-1) and nu4 (e, 1615.085 cm-1) have been recorded with a resolution of 3 x 10(-3) cm-1. The rovibrational analysis revealed severe perturbations of the -5