Palash P. Das

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 of NO2 at 6.2 μm

Abstract High-resolution spectra in the ν 3 region of 14 N 16 O 2 were measured by using a diode laser as a source to a vacuum grating spectrometer. Spin-rotation constants for the ν 3 and ν 2 + ν 3 states were determined from the observed data. Absolute strengths and transition moments for the ν 3 and ν 2 + ν 3 − ν 2 bands were derived from the observed line strengths at 296 K. Self-broadened and N 2 -broadened half-widths were measured for several of the ν 3 band lines at room temperature. Temperature-dependent half-widths for two N 2 -broadened ν 3 lines are also reported.

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 .

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.

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.

Tunable diode laser measurements of intensities and Lorentz broadening coefficients of lines in the ν2 band of 12CH4

Abstract Absolute line strengths and self-, nitrogen-, and air-broadened half-widths, for five lines in the R -branch of the ν 2 fundamental of methane have been measured at room temperature using a tunable diode laser spectrometer.

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

Diode laser spectroscopy of the ν6 band of 13CH3l and the ν″6 band of 12CH2Dl

Abstract The ν 6 band of 13 CH 3 I and the ν ″ 6 band of 12 CH 2 DI have been recorded under Doppler-limited resolution in the region 820–866 cm −1 using a tunable diode laser spectrometer. For 13 CH 3 I the constants for the ν 6 band were determined by simultaneous analysis of seven p Q ( J , K ) branches and several p P ( J , K ) and p R ( J , K ) transitions. For 12 CH 2 DI, the slight asymmetry introduced by the single D atom gives rise to noticeable asymmetry effects in the spectra of some of the p Q ( J , K ) subbands. From the analysis of six such subbands, the molecular constants for the ν ″ 6 level were determined.