M.D. Vanek

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.

Heterodyne measurements on N2O near 1635 cm−1

Abstract Heterodyne frequency measurements have been made on eight lines of the 10 0 0–01 1 0 band of N 2 O between 1591 and 1673 cm −1 . These measurements were combined with other heterodyne frequency measurements to obtain improved frequency values for the 01 1 0-00 0 0 transitions from 520 to 660 cm −1 .

Heterodyne frequency measurements of 12C16O laser transitions

Abstract This paper reports the first frequency measurements of a Lamb-dip-stabilized 12 C 16 O laser. The laser was stabilized to the optogalvanic Lamb dip of the CO molecule excited in a low-pressure dc discharge. The region of study was for transitions with lower state vibrational quantum numbers ranging from v ″ = 6 to v ″ = 16. Supplementary Doppler limited measurements are also reported for the range v ″ = 16 to v ″ = 34. The frequencies were directly measured in a heterodyne experiment in which two saturation-stabilized CO 2 lasers were used as references. By fitting the transition frequencies to the Dunham expression, we have determined new coefficients which fit the new sub-Doppler data with over an order of magnitude more accuracy than previous coefficients.

Heterodyne and FTS measurements on the OCS hot bands near 1890 cm−1

Abstract New infrared heterodyne frequency measurements are reported for carbonyl sulfide (OCS) near 1890 cm −1 . By combining these heterodyne measurements with microwave measurements reported in the literature and with new Fourier transform spectrometer measurements, we have determined rovibrational constants for the states involved in the following transitions: 02 0 1-00 0 0, 02 2 e 1-00 0 0, 03 1 1-01 1 0, 02 0 2-00 0 1, 04 0 1-02 0 0, 04 2 1-02 2 0, and 02 0 1-00 0 0 ( 16 O 12 C 34 S). New FTS measurements have also been made on the 03 1 2-01 1 1 band of the normal isotope, the 02 0 1-00 0 0 band of 16 O 13 C 32 S, and the 03 1 1-01 1 0 band of 16 O 12 C 34 S. The present frequency measurements have also been combined with other frequency measurements, reported earlier, to determine frequencies for the 02 0 2-00 0 0 transitions near 2730 cm −1 and the 04 0 1-00 0 0 transitions near 2940 cm −1 . A separate set of measurements was made to determine the pressure shift of the transitions in the 02 0 0-00 0 0 band of OCS. The shift is quite small, on the order of −0.4 ± 1.5 kHz/Pa (−0.05 ± 0.2 MHz/Torr).

Frequency measurements of high-J rotational transitions of OCS and N2O

Abstract A metal-insulator-metal diode has been used to generate far-infrared radiation as the difference between two CO2 lasers. With this technique rotational transitions of all the vibrational states below 2000 cm−1 have been measured for the normal isotopic species of OCS with an accuracy of 200 kHz or better. Transitions were measured primarily in the range from J = 65 ← 64 to J = 67 ← 66 but some measurements were also made from J = 91 ← 90 to J = 93 ← 92. Measurements are also given for the lower vibrational states of 16O12C34S in the range from J = 67 ← 66 to J = 69 ← 68 and for the normal isotopic species of N2O for J = 60 ← 59.

Heterodyne frequency and Fourier transform spectroscopy measurements on OCS near 1700 cm−1

Abstract Heterodyne frequency measurements are given for carbonyl sulfide (OCS) in the 1700 cm −1 region. The measurements were combined with Fourier transform spectroscopy measurements of the same bands and with other measurements in the literature (microwave, submillimeter wave, and other infrared measurements) in a least-squares fit. The combined data and fit result in improved frequency calibration values for the 1700 cm −1 region and also allow one to determine calibration values for the 00 0 3-00 0 0 band near 2550 cm −1 from application of the Ritz principle.

Heterodyne frequency measurements on N2O near 1060 cm−1

Abstract The results of heterodyne frequency measurements are given for the 10 0 0-02 0 0 band of N 2 O centered at 1056 cm −1 . Nine lines are measured and fit with an rms deviation of 1.3 MHz. The data are combined with other infrared and microwave data in a least-squares fit that gives accurate ro-vibrational constants for the two states involved in these transitions. The analysis of the data is based on a treatment that includes the effect of l -type resonance between the 02 0 0 and 02 2 0 states. Derived tables of wavenumbers are given for the 02 0 0-00 0 0 band near 1168 cm −1 and the 02 0 1-00 0 0 band near 2460 cm −1 .

Tunable Far Infrared Laser Spectroscopy

Tunable far-infrared (FIR) radiation has been generated using CO2 laser difference generation in metal-insulator-metal diodes either from the difference between a fixed frequency CO2 laser and a tunable waveguide laser, or from the difference between two fixed frequency CO2 lasers plus microwave sidebands. Our tunable FIR source is being used to make highly accurate FIR frequency measurements of stable species to serve as frequency and wavelength calibration standards; to measure frequencies of transient species (including molecular ions) for astronomical searches; and to study line broadening and line shape parameters especially for atmospheric spectroscopy applications.

Heterodyne measurements on OCS near 1372 cm−1

Abstract Heterodyne frequency measurements are given for the 01 1 1-00 0 0 and 02 0 -01 1 0 bands of OCS between 1363 and 1398 cm −1 . These measurements were combined with heterodyne measurements on the 01 1 1-01 1 0 and 02 0 1-00 0 0 bands to obtain frequencies for the 01 1 0-00 0 0 transitions by two independent paths. A table of wavenumbers is given for the ν 2 band of OCS from 488 to 557 cm −1 .

Pressure Dependent Lineshift Measurements on OCS

!A computer-controlled, frequency offset-locked spectrometer using a tunable diode laser is described and new measurements on carbonyl sulfide (OCS) are given to illustrate its use. Two OCS absorption lines, R( 3) and P( 30), have been measured for the 02°0-0000 vibrational transition near IO pm. An average pressure-induced shift coefficient of -0.37 * 0.04 kHz/Pa (-49 ? 5 kHz/Torr) was observed for the two lines. The self-broadening coefficient for each line has also been measured. 0 1991 Academic Press, Inc.