Sub-Doppler Measurements of the Rotational Spectrum of (13)C(16)O.

The five lowest J rotational transitions of (13)C(16)O have been measured by saturation-dip spectroscopy to an accuracy of about 2 kHz, employing phase-stabilized backward-wave oscillators (BWOs). These highly precise measurements cover the transitions from J = 2 <-- 1 to J = 6 <-- 5 with frequencies ranging from 220 to 661 GHz. For each of the five observed rotational transitions, the narrow linewidths of the saturation dips (about 20 kHz) permitted the resolution of the hyperfine splitting for the first time. This splitting is caused by the (13)C-nuclear spin-rotation interaction yielding a value for the nuclear spin-rotation coupling constant of C(I)((13)C(16)O). If combined with the beam measurements (C(I)((13)C(16)O) = 32.63(10) kHz), a slight J-dependence of the spin-rotation coupling constant can be determined (C(J) = 30 +/- 13 Hz). In addition, we have measured in the Doppler-limited mode several higher J rotational line positions of (13)C(16)O up to 991 GHz with an accuracy of 5 kHz. The two line positions (J = 12 <-- 11 and J = 14 <-- 13) were recorded by multiplying BWO frequency with an accuracy of 100 kHz. The rotational transitions J = 17 <-- 16 and J = 18 <-- 17 were measured with an accuracy between 15 and 25 kHz by using the Cologne sideband spectrometer for terahertz applications COSSTA. Copyright 2000 Academic Press.

Terahertz Spectroscopy of the Amidogen Radical, NH2.

The rotational spectrum of the NH2 radical in its &Xtilde;2B1 ground vibronic state was investigated between 614 and 1003 GHz. One hundred fifty-nine newly observed lines (188 hyperfine components) of six rotational transitions with 0

Millimeter and Submillimeter-Wave Spectrum of Hydrogen Peroxide in the Ground and v3 = 1 Vibrational States.

The first measurements of the millimeter- and submillimeter (mm/submm)-wave rotational-torsional transitions in the v3 = 1 ground torsional state (n = 0) of hydrogen peroxide are reported. The 149 newly measured transitions extend from 72 to 623 GHz in frequency and up to J = 32 and Ka = 3 in rotational quantum number. Additional measurements in the ground vibrational and torsional state around 1 THz are also reported. These data, along with all previously published microwave, mm/submm-wave, and far infrared data in the ground and v3 = 1 vibrational state, along with recent infrared measurements, have been fitted simultaneously to their respective experimental uncertainties using a multi-state Hamiltonian that includes Fermi- and Coriolis-type interactions. Copyright 1998 Academic Press.

High Frequency Transitions in the Rotational Spectrum of SO2.

A large number of rotational transitions of 32S16O2, 34S16O2, and 32S18O16O have been measured in the mm-, submm-, and terahertz ( approximately 1 THz) spectral regions. These data sets have been combined with all previously measured SO2 microwave and selected far infrared data to obtain a highly precise set of ground state rotational constants for these isotopomers. The rotational constants for the three isotopomers are in MHz as follows: Parameter32S16O234S16O232S18O16O A60778.54977 (44)58991.18295 (51)59101.1690 (27) B10318.07348 (7)10318.50993 (9)9724.64284 (56) C8799.703399 (70)8761.302481 (97)8331.56018 (51) Centrifugal distortion constants up to P10 are included in the fit. A frequency listing of all the data used in the frequency range between about 7 GHz and 1 THz is included. Copyright 1998 Academic Press.

Hyperfine Structure of Rotation-Inversion Levels in the Excited nu2 State of Ammonia

Hyperfine structures of the rotation-inversion transitions with J = 3 <-- 2, s <-- a, and K = 0, 1, 2, and with J = 0 <-- 1, a <-- s, and K = 0 in the excited nu2 vibrational state have been resolved and measured by sub-Doppler saturation spectroscopy using the Cologne terahertz spectrometer with an accuracy of about 1 kHz. The line frequencies of the hyperfine structures of the rotation inversion transitions (at 466, 769, 742, and 763 GHz) have been simultaneously analyzed with the previously published J = 2 <-- 1, s <-- a, K = 1, nu2 transition in terms of effective nuclear quadrupole and spin-rotation parameters. The corresponding pure rotation-inversion frequencies, deperturbed from the hyperfine effects, have also been derived. Copyright 1998 Academic Press.

Precise Measurement of the Pure Rotational Submillimeter-Wave Spectrum of HCl and DCl in Their v = 0, 1 States

High-resolution sub-Doppler Lamb-dip measurements were performed on the low-J pure rotational transitions of the hydrogen chloride isotopomers H35Cl, H37Cl, D35Cl, and D37Cl in the submillimeter-wave region up to 646 GHz. For the J = 1-0 transitions of the two HCl isotopomers, the hyperfine splitting due to the hydrogen nuclear spin-rotation interaction is resolved. Furthermore Doppler-limited lines of the DCl J = 3 <-- 2 transition around 965 GHz as well as hyperfine-resolved rotational transitions in the first excited vibrational state were recorded up to 1.22 THz. The new frequencies were analyzed in a global fit together with FIR data yielding a set of mass-invariant rotational parameters. Isotopically invariant hyperfine parameters were obtained also from the global fit. Inclusion of the precise results from molecular beam electric resonance measurements allowed the determination of higher orders of the vibrational and rotational expansion coefficients of the chlorine and hydrogen hyperfine interactions. The precise transition frequencies reported here should be useful as secondary calibration standards in the submillimeter-wave and terahertz region. Copyright 1998 Academic Press. Copyright 1998Academic Press

33SO2: Interstellar Identification and Laboratory Measurements

The rotational spectrum of 33S isotopically substituted sulfur dioxide, 33SO2, has been measured up to nearly 1 THz. The combined analysis of these new data together with the published line frequencies resulted in refined molecular constants, such as the rotational (A = 59856.4723(62) MHz, B = 10318.3012(15) MHz, C = 8780.1363(15) MHz) and centrifugal distortion constants which yielded precise frequency predictions. The carrier of six previously unidentified interstellar lines in the Caltech molecular line survey in the 325-360 GHz band could be assigned to 33SO2. Copyright 1997 Academic Press. Copyright 1997Academic Press

Submillimeter-Wave Rotational Spectra of SO Isotopomers in the Electronic States a1Delta and b1Sigma+

Pure rotational transitions of the sulfur monoxide isotopomers 32S16O, 34S16O, and 32S18O were measured in different vibrational states of the electronic states a1Delta and b1Sigma+ with the Cologne terahertz spectrometer in the submillimeter-wave region between 300 and 1070 GHz. The new lines were analyzed together with previous results from the literature in a global fit yielding isotopically invariant rotational parameters for both states. The measurements reported here allowed for the first time the determination of the parameters U01S and U01O to correct for the breakdown of the Born-Oppenheimer approximation analogously to the X3Sigma- state. Precise equilibrium bond lengths re are given for all states concerned. Copyright 1997 Academic Press. Copyright 1997Academic Press

Pure Rotational Spectra of SO: Rare Isotopomers in the 80-GHz to 1.1-THz Region

Pure rotational spectra of rare isotopomers of sulfur monoxide, SO, have been recorded with the Cologne Terahertz Spectrometer, Germany, and the millimeter- and submillimeter-wave spectrometer at Nobeyama, Japan. In total, 176 new transitions have been measured in the X3Sigma- electronic ground state, including the first laboratory detection of the rare isotopomer 36SO. New lines are also reported for 33SO and S17O in their vibrational ground states, and for 33SO and S18O in the first excited vibrational state. A simultaneous fit of 451 transitions has led to an improved set of isotopically invariant parameters for rotation and fine structure. Hyperfine structure constants for 33SO and S17O have been obtained also from the global fit, including first values for the magnetic nuclear spin-rotation interaction. These are compared to other molecules. The isotopically invariant parameters allow precise frequency predictions for the submillimeter-wave region far beyond 1 THz for all SO isotopomers, of importance to astrophysical applica- tions.