K. Narahari Rao

The low-frequency vibration rotation bands of the ammonia molecule

Abstract The absorption spectra of ammonia from 1440 cm −1 to 1840 cm −1 and from 510 cm −1 to 1280 cm −1 have been obtained with a vacuum grating spectrometer. The frequencies of the observed lines are given and the energy levels for the ν 4 , ν 2 , and 2 ν 2 vibration-rotation modes computed. A theoretical discussion of the Coriolis interaction between the ν 2 and ν 4 band and the “giant” l-type doubling observed in the ν 4 band is given and the results applied to the observed data.

Coriolis and l-type interactions in the ν2, 2ν2, and ν4 states of 14NH3

High-resolution infrared spectra have been remeasured for the ..nu../sub 2/, 2..nu../sub 2/, and ..nu../sub 4/ bands of /sup 14/NH/sub 3/ using a vacuum grating infrared spectrometer and a diode laser spectrometer. Far-infrared spectra of /sup 14/NH/sub 3/ have been measured with microwave accuracy in the 700 to 1100 GHz region by employing a submillimeter wave spectrometer (RAD) with acoustic detection. The pure inversion and inversion-rotation transition frequencies in the ..nu../sub 2/ excited state of /sup 14/NH/sub 3/ have been determined for the first time. The vibration-inversion-rotation Hamiltonian of ammonia reported by Spirko, Stone, and Papousek has been used for a precise parameterization of the energy levels of ammonia. The ground state rotational and centrifugal constants of /sup 14/NH/sub 3/ have been determined using a modified method of combination differences. Coriolis and l-type interactions between ..nu../sub 2/, ..nu../sub 4/, 2..nu../sub 2/, ..nu../sub 2/ + ..nu../sub 4/, and 3..nu../sub 2/ states have been analyzed and the band parameters have been obtained which reproduce the transition frequencies within the accuracy of the experimental data.

Investigations of several infrared bands of 12C2H2 and studies of the effects of vibrational rotational interactions

Twenty seven infrared bands of acetylene (12C2H2) in seven selected regions have been measured with high resolution vacuum spectrographs. Some of these have been studied for the first time under high resolution, several molecular constants have been determined with improved accuracy and the rotational assignments have been corrected in a few instances. The need to determine the relative orientations of the Δ states from experimental studies has become evident in recent work related to C2D2 and C2HD spectra. In the present investigation, for the two Δ states 0000022 and (00011)2 the c component has been found to be higher than the corresponding d component. For the first time, a Π state has also been established to have the same feature; normally, in the case of Π states the Πd component is higher than the Πc.

Infrared bands of 12C2HD

Abstract The rotational structure of about 40 bands of 12C2HD observed in the region 6000−600 cm−1 has been measured and interpreted with the purpose of determining a comprehensive set of molecular constants for this isotopic variety of acetylene. Combining these data with the results for 12C2H2 and 12C2D2, a reevaluation of the equilibrium internuclear distances for the acetylene molecule has been made: r e (CH) = 1.06215 ± 17 × 10 −5 A and r e (CC) = 1.20257 ± 9 × 10 −5 A were obtained. This paper presents all the molecular constants derived in this study.

Vibration rotation bands of heated hydrogen halides

Abstract The higher J rotational structure of the near infrared bands of HF, HCl, and DCl has been measured. The values of Y 10 (≡ ω e ) and Y 01 (≡ B e ) for HF are calculated as 4138.32 ± 0.06 cm −1 and 20.9557 ± 0.0009 cm −1 , respectively.

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.

Spectrum of water vapor in the 1.9 and 2.7μ regions

Abstract The rotational structure of the ν 1 , ν 3 , 2 ν 2 , ν 1 + ν 2 , and ν 2 + ν 3 bands of water vapor has been recorded using a high resolution vacuum infrared spectrograph. Values for the energy levels of the ground vibrational state and of the upper states of these bands have been determined. Several intensity anomalies have been observed in lines previously assigned to the ν 1 , ν 3 , and 2 ν 2 bands. Experimental results for these intensity anomalies have been presented.

Interpretation of the acetylene spectrum at 1.5 μm

Abstract Bands of acetylene in the region 6680-6460 cm −1 recorded with a high resolution infrared spectrograph are assigned to transitions and molecular constants of the levels involved have been evaluated.

High resolution infrared spectra of water vapor: ν1 and ν3 bands of H218O☆

Abstract The ν1 and ν3 bands of H216O occurring in the region 2.5–3.0 μ were recorded with a high resolution vacuum infrared spectrograph and an analysis has been presented of the rotational structure observed. The present study led to the determination of accurate values for the ground state energy levels of the H216O molecule. The band origins obtained are: ν1 = 3657.050 cm−1 and ν3 = 3755.970 cm−1. A discussion is presented of the effects of perturbations between the upper states of the transitions involved.