V. Malathy Devi

Analysis of high resolution fourier transform and diode laser spectra of the ν9 band of ethane

Abstract Fourier transform measurements with an apodized apparatus function up to 0.002 cm−1 are reported for the ν9 band (ρu) of ethane in the 12-μm region, together with an integrated band strength obtained from intensity measurements on selected Q-branch lines recorded using a diode laser spectrometer. Since the ν9 band falls in an atmospheric window, these data may be useful in studies of the ethane concentration in the atmosphere of Jupiter and other outer planets. Torsional splittings in the ν9 level caused by a higher-order Coriolis interaction with the close lying 3ν4 state (a1u) have been analyzed in a global least squares fit of 2206 Fourier transform lines and 58 diode splittings to a molecular Hamiltonian containing 20 parameters, with a standard deviation of 0.35 × 10−3 cm−1. Rotational levels of one component of the torsionally split 3ν4 state cross interacting rotational levels of the ν9 state for K = 17, and the spectrum is followed to K = 19 on the pP subband side to permit inclusion of ν9 levels beyond this crossing. No transitions to 3ν4 levels were observed. The theoretical treatment presented here makes use of standard symmetric top formalism and of the G 36 † double-group formalism for ethane.

Tunable diode laser spectroscopy in the infrared: some practical considerations of techniques and calibration with ν 2 lines of HCN

A tunable diode laser has been incorporated as a source in an operating high resolution vacuum grating spectrometer. The advantages of such a system for recording molecular spectra have been elaborated. In the process of developing this system, several practical problems came about, and it has been considered useful to document the manner in which they have been resolved. In particular, for work in the region of 15 microm, it was advantageous to develop an air-spaced Fabry-Perot etalon to record fringes simultaneously with the scanning of molecular spectra. This was successfully done, and the upsilon(2) band lines of the HCN molecule at 14 microm have proved to be ideally suited for determining the fringe spacing spectroscopically.

Spectrum of phosphine at 4 to 5 μm: Analysis of ν1 and ν3 bands

Abstract The absorption spectrum of phosphine has been investigated in the region 2087–2482 cm−1. About 1200 transitions belonging to the bands ν1 and ν3 were assigned. A strong Coriolis interaction between these bands gives rise to many “forbidden” transitions and large A1A2 splittings. The simultaneous analysis of the two bands enabled us to get a set of vibration-rotation constants for the vibrational states v1 = 1 and v3 = 1, and to obtain a value for the ratio S 1 S 3 between the band strengths of ν1 and ν3.

Diode laser measurements of intensities, N2-broadening, and self-broadening coefficients of lines of the ν2 band of 14N16O2

Abstract A diode laser spectrometer (resolution 0.0013 cm −1 ) was used to record, in the 12-μm region, high-quality spectra of the ν 2 band of NO 2 . Using these spectra, it was possible to obtain the N 2 -broadening coefficients and an average self-broadening coefficient from measurements made for seven lines of this band. In addition, 30 single spin-component line intensities were measured. From them, through a least-squares fit, the purely vibrational transition moment of the ν 2 band, as well as two correcting rotational terms involved in the expansion of the transition moment operator, were obtained. These results led to the determination of the dipole moment derivative ∂μ x ∂q 2 = −0.0604 1 ± 0.0037 D . It was also demonstrated that there is good consistency between the correcting terms deduced from the observed intensities and their theoretical estimates. Finally, a complete spectrum of the ν 2 band of NO 2 was computed, providing a total band intensity S v ( ν 2 ) = 0.542 × 10 −18 cm −1 /molecule cm −2 at 296 K.

Diode laser spectra of the ν2 band of 14N16O2: The (010) state of NO2

Abstract Diode laser spectra of the ν 2 band of NO 2 are recorded and analyzed. Due to the very high resolution (0.002 cm −1 ), the Q branches are completely resolved. Although the whole ν 2 band is not completely covered, the quality of the spectra led to an improved set of rotational and spin-rotation constants. The band center is found to be ν 2 = 749.6541 ± 0.0012 cm −1 .

Absorption spectrum of carbon dioxide at 4.3 μm

Abstract The absorption spectrum of carbon dioxide has been recorded in the wavenumber region 2395-2216 cm −1 with a spectral resolution between 0.02 and 0.03 cm −1 . About twenty transitions have been identified and the molecular constants of the levels involved have been evaluated. In view of the interest of this region in atmospheric studies a map of the entire spectrum recorded by using a normal sample of carbon dioxide is presented including the identifications for the different bands. About 90% of the lines observed have been interpreted. Some of them have been assigned to transitions originating from higher excited states of 12 C 16 O 2 not considered before in interpreting this spectral region. For the first time, bands of 12 C 16 O 17 O have been identified in the 4.3-μm spectra obtained with the natural sample.

Diode laser spectroscopy of the ν6 band of 12CH3I

Abstract The vibration-rotation spectrum of the ν 6 fundamental of methyl iodide has been recorded in the 824 to 862 cm −1 region by using a tunable semiconductor diode laser spectrometer. The rotational analysis performed for six Q branches p Q ( J ,3), p Q ( J ,4), p Q ( J ,5), p Q ( J ,6), p Q ( J ,7), and q Q ( J ,8) led to accurate values for several molecular constants. The nuclear quadrupole splitting arising from the spin of iodine has been observed very clearly in the low J transitions and for various K values.

Interpretation of the 13C16O2 spectrum at 4.4 μm

Abstract The overlapping structure observed in the region of the ν 3 fundamental of 13 C 16 O 2 at 4.4 μm has been assigned to several transitions belonging to not only the 13-C variety of carbon dioxide ( 13 C 16 O 2 ) but also to 13 C 16 O 17 O and 13 C 16 O 18 O species occurring in the sample. Molecular constants have been evaluated for the assigned transitions.

The diode laser spectrum of the ν2 band of 14ND3 and 15ND3

Abstract The spectra of the ν 2 bands of 14 ND 3 and 15 ND 3 were measured under Doppler-limited resolution with a diode laser spectrometer in order to resolve the K structure of the sR ( J , K ) and aR ( J , K ) multiplets. By a simultaneous least-squares analysis of these data, the Fourier spectra of the ν 2 band measured by Jones [ J. Mol. Spectrosc. 74, 409 (1979)], and the ground-state microwave transitions, sets of improved ν 2 -band parameters were obtained, including the sextic centrifugal distortion coefficients.

Convolution of a Doppler line by a Gaussian instrument function

A simple and direct method is obtained for assessing the distortion of a Doppler line by a Gaussian instrument function. It is suggested that a close approximation to the width of a Gaussian instrument function, or an almost Gaussian function, may be obtained by measuring a line with a Doppler absorption coefficient. The method is applicable to diode laser measurements, and may be used whenever a Gaussian instrument function is a reasonable approximation to real conditions