The J=0–1 rotational transition of XeH+ and the J=1–2 transition of XeD+, which both occur near 390 GHz, have been studied by microwave absorption spectroscopy. For each of these all nine naturally occurring stable isotopes of xenon were detected. The magnetic hyperfine structure for the 129Xe forms and the electric quadrupole–magnetic hyperfine structure of both 131Xe forms were fully resolved and analyzed to determine the CI and eQq0 constants. The scaled spin–rotation parameter CI/(gIB) is found to be practically identical in XeH+ and HI, as it is also in the isoelectronic pair KrD+ –DBr/HBr. The available magnetic field was too small to resolve the rotational Zeeman effect, but the rotational g factor of XeH+ was estimated from Zeeman broadening. The mass-independent Dunham parameters U01, ΔH01, and ΔXe01 were determined from the very accurate microwave frequencies combined with higher order Dunham coefficients from published Fourier-transform infrared (FTIR) spectroscopy of XeH+ . Although it was not practical to observe XeH+ or XeD+ in excited vibrational states, we were able to detect the J=0–1 (v=1) transition of ArD+ .
The 110←111 transition of H2D+ was detected in a dc discharge in Ar–H2–D2 mixtures with liquid nitrogen cooling and an applied axial magnetic field. The transition frequency was determined to be 372 421.380±0.100 MHz. This transition is expected to be the most favorable one for radioastronomical detection of this very crucial ion in the interstellar medium.
The microwave spectrum of PO+ has been detected in discharges in mixtures of PF3, O2, and Ar. Precise frequencies were obtained for 48 rotational transitions in the range 140–470 GHz, including all vibrational states v=0–11. Eight of the lines measured were transitions of P18O+, obtained using 18O2. To fit all of these to a mass independent Dunham expansion, a Watson ΔO01 parameter was required to describe the oxygen isotope shift. From the combined analysis a set of eight mass independent Dunham parameters Ukl and the Dunham potential constants a1–a5 were extracted. Harmonic and anharmonic vibrational constants are obtained from the microwave analysis and compare very well to published results from low resolution emission spectroscopy; the final microwave values of re and ωe are 1.424 992 7(4) Å and 1411.5(3) cm−1. These and the a1–a5 coefficients are in very good agreement with the results of several ab initio calculations we have done on PO+ (and other 22 electron diatomics), including those that were used to define the limits of our initial search for the microwave spectrum of PO+. The vibrational temperature of PO+ in our magnetically enhanced negative glow discharge was found to be very high, near 5500 (500) K. Some additional observations of the microwave spectrum of SiF+, used as a probe of the dynamical and chemical behavior of SiF+ in discharges, are also reported.
The first detection of the silicon monofluoride cation by spectroscopic means has been achieved at millimeter and submillimeter wavelengths. Frequencies of rotational transitions spanning a range of J values from 1 to 14 and all vibrational states from v=0 to 15 were precisely measured. Lines of 29 SiF+ up to v=4 and 30 SiF+ up to v=3 were also included in this study. These data were all well fit by a standard Dunham expansion with eight terms, with no requirement for a Watson type ΔSi01 parameter, describing breakdown of the Born–Oppenheimer approximation, to explain the isotope dependence. The parameters Be (or re ), ωe , and the Dunham potential constants a1 –a5 were well determined from this analysis and showed very satisfying agreement with the results of our recent large basis set MP4SDQ and CI calculations, which we had used to determine the search range for locating the spectrum of SiF+ . The final results are re =1.526 495 0(2) Å and ωe =1050.7(2) cm−1.
The first detection of SiF+ by spectroscopic means is achieved at millimeter and submillimeter wavelengths.
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