Lyndon R. Zink

Accurate rotational constants of CO, HCl, and HF: spectral standards for the 0.3-to 6-THz (10- TO 200-cm−1) region

Abstract Accurate high-resolution spectroscopic measurements require secondary standards which can serve as convenient calibration references in laboratory and field research. We have measured the frequencies of a series of rotational transitions between 0.3 and 6 THz for several stable and readily obtainable gases (CO, HCl, and HF) to an accuracy better than one part in 10 7 and present revised rotational constants for these molecules. The gases were selected (in part) due to their presence in the Earths atmosphere in significant amounts and thus are convenient for the frequency calibration of atmospheric spectra.

Continuous-wave frequency tripling and quadrupling by simultaneous three-wave mixings in periodically poled crystals: application to a two-step 1.19–10.71-µm frequency bridge

We observed cw third-harmonic generation in a periodically poled LiNbO(3) crystal by cascading optimally phase-matched second-harmonic and sum-frequency generation. Other processes, such as fourth-harmonic generation, are allowed by the flexibility of quasi-phase matching. We demonstrate a divide-by-nine (1.19- 10.71-microm) frequency chain that uses only two lasers.

Methanol and the optically pumped far-infrared laser

New results on the generation and spectroscopic analysis of optically pumped far-infrared (FIR) laser emission from CH/sub 3/OH have been obtained as part of a systematic study of methanol isotopomers as FIR laser sources utilizing the extended line coverage available from a recently developed high-resolution CO/sub 2/ laser of high efficiency. For normal CH/sub 3/OH, six new short-wavelength lines have been found using a 2 m long Fabry-Perot FIR laser cavity. Accurate heterodyne frequency measurements are reported for 14 CH/sub 3/OH FIR laser lines, nearly all above 100 cm/sup -1/, as well as accurate frequency offsets for most of the corresponding CO/sub 2/ pump lines. Spectroscopic assignments are presented for nine high-frequency FIR laser lines in four pump systems.

Measurement of high-frequency rotational transitions of H2O+ in its ground state by far-infrared laser magnetic resonance (LMR) spectroscopy

Thirteen new rotational transitions of H2O+ in the (0,0,0) level of the X 2B1 state have been measured in the wavenumber region between 80 and 200 cm−1 (50 and 120 μm) by far-infrared laser magnetic resonance (LMR) spectroscopy. LMR data measured previously between 25 and 90 cm−1 (110 and 400 μm), as well as optical and infrared combination differences, have been combined with the new LMR data in a weighted least-squares analysis using an A-reduced expression of the rotational-fine structure Hamiltonian. Thirty-two molecular constants were simultaneously determined, some sextic centrifugal distortion parameters and some quartic and sextic spin-rotation parameters for the first time. From this improved set of molecular parameters, very accurate calculations of rotational term values and zero-field predictions of the 111–000 transition, including hyperfine structure, have been performed. Moreover, the electronic g-tensors and the hyperfine coupling constants are consistent with ab initio calculations which...

Pure rotational far-infrared transitions of 16O2 in its electronic and vibrational ground state

Abstract Five lines in the far-infrared region, due to N + 2 ← N (Δ J = 0) transitions of the 16 O 2 molecule in its ( X 3 Σ g − , v = 0) state, are measured at 773.839691, 1466.807133, 1812.405539, 2157.577773, and 2502.323923 GHz, using a tunable FIR spectrometer. The spectral lineshape of the 2.50-THz line is analyzed and the pressure self-broadening parameter of 18.2(32) kHz/Pa (=2.43(43) MHz/Torr) is obtained.

High-resolution spectroscopy of HF from 40 to 1100 cm−1: Highly accurate rotational constants

Abstract Highly accurate spectra of ground state rotational transitions in HF have been combined with earlier spectra to yield accurate rotational constants and frequencies of HF from 1 to 33 THz (40 to 1100 cm−1). These lines can be used for accurate secondary frequency references for IR and FIR spectroscopy. Direct frequency measurements provided the references for the most accurate of these data.

Atomic oxygen fine-structure splittings with tunable far-infrared spectroscopy

We have accurately measured fine-structure splittings of atomic oxygen (l60) in the ground state using a tunable far-infrared spectrometer. The 3P,-3P, splitting is 2,060,069.09 (10) MHz, and the 3P1-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in Earths atmosphere and the interstellar medium. Subject headings: infrared: spectra - interstellar: matter - laboratory spectra - planets: atmospheres

The far infrared spectrum of magnesium hydride

The rotational spectrum of MgH in its ground 2∑ state has been observed for the first time using a new tunable far infrared spectrometer. The molecular constants derived are of sufficient accuracy to permit astrophysical identification of this species.

Tunable far-infrared spectroscopy extended to 9.1 THz

We synthesized tunable far-infrared radiation at frequencies higher than 9 THz (300 cm (-1)) by mixing CO(2) laser, (15)NH(3) laser, and microwave radiation in a W-Co metal-insulator-metal diode. We used this farinfrared radiation to accurately measure torsion-rotation transitions of CH(3)OH in the 8-9-THz region. We also measured the frequency of the aP(7, 3) (15)NH(3) laser transition.

Vibrational structure in the laser excitation spectrum of nickel dichloride at 360 nm

Abstract Nickel dichloride has been formed “cold” in the vapor phase by heating the solid to about 750°C, entraining the vapor in a high pressure of argon and expanding it supersonically through a small hole into a vacuum chamber. The laser excitation spectrum of the sample prepared in this way has been recorded in the region of 360 nm. Under these conditions, it is possible to resolve both vibrational and rotational fine structure. The same spectrum was recorded when carbon tetrachloride vapor was passed over the hot metal and expanded through the nozzle. Some “hot” bands have been identified by dispersing the fluorescence with a small monochromator. Virtually no chlorine isotope structure could be identified, even when isotopically enriched samples were used. A partial analysis of the vibrational structure has been achieved in which several progressions in the symmetric stretching vibration have been identified. These progressions are consistent with a value for v 1 of 360 cm −1 for the lower electronic state and 345 cm −1 for the upper electronic state. The complications in the observed spectrum may be caused by two or more upper electronic states being involved in the band system.