J. Kauppinen

A simultaneous analysis of the microwave, submillimeterwave, far infrared, and infrared-microwave two-photon transitions between the ground and ν2 inversion-rotation levels of 14NH3

Abstract Fourier transform infrared spectra of the inversion-rotation transitions have been measured with 0.010-cm −1 resolution between 40 and 300 cm −1 in the ground state and ν 2 excited states of 14 NH 3 . Submillimeterwave spectra of the inversion and inversion-rotation transitions in the ν 2 state of 14 NH 3 , including a few Δ k = ±3 “perturbation-allowed” transitions, have been measured with microwave accuracy between 540 and 770 GHz. A simultaneous least-squares analysis of these data, the microwave ground-state transition frequencies, and the ν 2 infrared-microwave two-photon transition frequencies has been carried out. A theory of the Δ k = ±3 n interactions in the ground and ν 2 excited states of ammonia (S. P. Belov, L. I. Gershtein, A. F. Krupnov, A. V. Maslovskij, S. Urban, V. Spirko, and D. Papousek, J. Mol. Spectrosc. 84 , 288–304 (1980)) has been used in the analysis. A set of the ground- and ν 2 -state molecular parameters has been obtained which describes the experimental data within the precision of the experiment. The “smoothed” values of transition frequencies can be used for calibration purposes with a precision better than 3 × 10 −5 cm −1 in the submillimeterwave region, better than 10 −3 cm −1 in the far-infrared region, and better than 1.5 × 10 −3 cm −1 in the region 700 – 1200 cm −1 .

High-resolution spectrum of water vapor between 30 and 720 cm−1

Abstract The pure rotational spectrum of natural water vapor between 30 and 720 cm−1 has been recorded by a double-beam Fourier spectrometer. The maximum resolution achieved was about 0.018 cm−1 and the accuracy of the observed line positions was better than ±0.001 cm−1 in favorable conditions. The 550 line positions observed have been compared with the values derived from rotation-vibration spectra. The strongest lines of the isotopic molecules H218O, H217O, and HD16O have been identified and many rotational transitions in the vibrational level (010) have also been assigned.

The ν2 band of 14NH3: A calibration standard with better than 1 × 10−4 cm−1 precision

Abstract The Fourier transform spectra and the diode laser spectra of the ν2 band of 14NH3 have been measured with 0.005 and 0.002 cm−1 resolution, respectively. A simultaneous least squares analysis has been carried out of these data together with the microwave, submillimeterwave, diode-laser heterodyne, and infrared-microwave two-photon transition frequencies between the ground and the ν2 inversion-rotation levels. A theory of the Δk = ±3n interactions in the ground and ν2 excited states of ammonia (S. Urban, V. Spirko, D. Papousek, J. Kauppinen, S.P. Belov, L. I. Gershtein, and A. F. Krupnov, J. Mol. Spectrosc. 84, 288–304 (1981)) has been used in the analysis. The “smoothed” values of the ν2 band wavenumbers can be used for calibration purposes with better than 1 × 10−4 cm−1 precision. On the basis of these results, a critical evaluation has been carried out of several experimental techniques of very high resolution infrared spectroscopy.

Infrared spectrum of CO2 in the region of the bending fundamental ν2

Abstract The infrared spectrum of CO 2 in the region 540–830 cm −1 has been studied with a Fourier spectrometer at a resolution of 0.010 cm −1 . In addition to the fundamental ν 2 , more than 10 “hot” band transitions of 12 C 16 O 2 have been identified. The rotational constants involved have been derived. Special care has been taken in obtaining accurate constants for the level 01 1 0. The ν 2 fundamentals of the isotopic molecules 13 C 16 O 2 , 16 O 12 C 18 O, and 16 O 12 C 17 O have also been observed in a natural sample.

Double-beam high resolution Fourier spectrometer for the far infrared.

The construction and the performance of a double-beam Michelson-type Fourier spectrometer are described. The instrument covers a wavenumber range from 10 cm(-1) to 450 cm(-1) with a maximum resolution of 0.025 cm(-1) and an accuracy of frequency within +/-0.001 cm(-1). The optical path difference is measured by means of an He-Ne gas laser. To illustrate the general performance of the instrument, the pure rotational spectra of H(2)O and CO have been recorded.

High-resolution infrared spectrum of acetylene in the region of the bending fundamental v 5

The infrared spectrum of C2H2 in the region of the bending fundamental v 5 has been studied at a resolution of about 0·015 cm-1. The molecular constants G 0(v 5=1) = 730·3341 (1) cm-1 and B 0 = 1·176641 (2) cm-1 have been derived. In addition to the fundamental, all the hot bands starting from the levels v 4 and v 5 have been investigated. The vibrational, vibration-rotation coupling and centrifugal constants for the excited vibrational states v 5 = 2 and v 4 = v 5 = 1 have been derived using the vibration-rotation energy matrix.

New wave-number calibration tables for H 2 O, CO 2 , and OCS lines between 500 and 900 cm −1

The pure rotational lines of H(2)O, the nu(2) band of CO(2), and the nu(1) band of OCS were simultaneously recorded by a Fourier transform spectrometer. The resolution achieved was ~0.0045 cm(-1), and the precision of the line position was typically 3.6 x 10(-5) cm(-1) or 1.2 MHz (standard deviation). The spectrum improves the accuracy of wave numbers of calibration lines in the region between 500 and 720 cm(-1) by a factor of ~10.

Smoothing of spectral data in the Fourier domain.

Smoothing of spectral data using Fourier transforms is described and demonstrated with Lorentzian, sinc(2), and sine smoothing functions. Four parameters are defined and used to study the smoothing operation. It is also concluded that the best smoothing function is a sinc function if we require that the distortions due to the smoothing operation are smaller than the residual noise. Sine smoothing using Fourier transforms is also compared to least square smoothing in the frequency domain, and the advantages of sine smoothing are illustrated.

Working resolution of 0.010 cm −1 between 20 cm −1 and 1200 cm −1 by a Fourier spectrometer

The original double-beam Michelson-type Fourier spectrometer at the University of Oulu has been partly modified so that a maximum resolution of slightly better than 0.010 cm(-1) between 20 cm(-1) and 1200 cm(-1) can be obtained. The resolution is determined as a halfwidth of an observed line. The accuracy of the line position is 0.0005 cm(-1) in favorable conditions. The Fourier spectrometer is connected on-line to a minicomputer, in order to make the fast Fourier transforms of interferograms of up to 10(6) sampling points. The maximum optical path difference of the interferometer is about 1.5 m, giving a maximum theoretical resolution of 0.004 cm(-1).

ν7 and ν9 bands of formic acid near 16 μm

Abstract The ν 7 and ν 9 fundamental bands of formic acid were studied by Fourier transform spectroscopy with a resolving power of 0.020 cm −1 . Band centers obtained are ν 7 = 626.158 cm −1 and ν 9 = 640.722 cm −1 . It was possible to determine rotational and centrifugal distortion parameters for both vibrational states v 7 = 1 and v 9 = 1 and also the two first-order Coriolis interaction parameters along z and x axes and the second-order Coriolis parameter along z axis. The stability of rotational and distortion parameters compared to ground state values confirms that a Watson type Hamiltonian is well adapted to such a problem.