R. H. Schwendeman

Investigation of the ν5 band of methylacetylene by infrared laser Stark and microwave spectroscopy

Abstract Microwave spectra have been studied in the ground and v 5 = 1 (CC stretching mode) states of methylacetylene. From these data, dipole moments and rotational and centrifugal distortion constants have been determined, as follows: μ D (0) = 0.7839 ± 0.0010 D, μ D (5) = 0.7954 ± 0.0010 D, B 5 = 8508.119 ± 0.003 MHz, D J (5) = 1.8 ± 0.2 kHz, and D JK (5) = 169 ± 1 kHz. Laser Stark spectra have been obtained for the ν 5 band of this molecule and from these spectra the following vibration-rotation parameters have been determined: ν 5 0 = 93.27540 ± 0.00007 cm −1 , A 5 - A 0 = −227.0 ± 2.3 MHz and D K (5) - D K (0) = −0.05 ± 0.50 MHz. The higher- J and - K states of the v 5 = 1 state appear to be purturbed.

High-resolution Fourier transform spectroscopy of D2CO in the 8- to 12-μm region☆

Abstract The Coriolis-coupled ν 3 (1100 cm −1 ), ν 6 (989 cm −1 ), and ν 4 (938 cm −1 ) fundamental bands of D 2 CO have been recorded with a BOMEM Model DA 3.002 Fourier transform spectrometer at an apodized resolution of 0.004 cm −1 . A total of 3704 transitions have been assigned in the 780- to 1200-cm −1 spectral region. Constants have been determined for terms up to P 6 in centrifugal distortion and up to P 3 in Coriolis interaction. These constants reproduce the observed spectra with residuals for well-resolved lines that are less than 0.0004 cm −1 , one-tenth of the resolution. Relative signs of the transition moments have been determined by comparison of observed and calculated relative intensities of perturbed transitions. Five new assignments for far-infrared laser lines pumped by CO 2 lasers have been obtained as a result of calculations based on the determined constants.

Infrared microwave sideband laser spectroscopy of the ν3 and 2ν3 ← ν3 bands of 13CH3F☆

Abstract A large number of transitions in the ν 3 and 2 ν 3 ← ν 3 bands of 13 CH 3 F have been recorded at Doppler-limited resolution by means of an infrared laser microwave sideband spectrometer. The sidebands were generated in a CdTe crystal that was simultaneously irradiated by a CO 2 infrared laser and a high-power microwave source operating in the 8- to 18-GHz region. The J and K structures of the bands were well resolved except for the lowest K values. Frequencies of transitions involving J values up to 47 and K values up to 16 are reported. Vibration-rotation parameters for the v 3 = 0, 1, and 2 states were obtained by fitting to the experimental frequencies. These parameters reproduce the experimental values with an rms deviation of 3.8 MHz for the fundamental band and 2.5 MHz for the hot band.

The microwave spectrum of vinylcyclopropane

Abstract Frequencies of rotational transitions in the microwave region are reported for the ground and three torsionally excited states of the species of vinylcyclopropane in which the vinyl group is trans to the cyclopropane ring and there is a plane of symmetry. Transitions in the species with 13 C substitution at the out-of-plane carbon site are also reported. An extensive search for transitions belonging to another species was not successful. The torsional excitation energy is estimated from relative intensity measurements to be 125 cm −1 . The dipole moments determined from the Stark effect ar μ a = 0.486 ± 0.007 D, μ c = 0.110 ± 0.010 D and μ = 0.498 ± 0.007 D.

Infrared-microwave two-photon spectroscopy of the ν2 band of 14NH3

Abstract Transitions in the ν2 band of 14NH3 were recorded by means of an infrared laser microwave two-photon spectrometer. The spectrometer, which uses a minicomputer to step the microwave frequency and record the spectrum, is described. With sample cells outside the laser cavity good lineshapes are obtained, so that the accuracy of frequency measurement was limited by the resettability of the CO2 or N2O lasers employed, ∼0.0002 cm−1. The present data are compared to previously obtained results based on CO2 or N2O laser frequencies and to recently reported calculations. Rotational constants derived for the hypothetical inversion-free ground and v2 = 1 states are reported.

Infrared-microwave two-photon spectra of the ν3 bands of 12CH3F and 13CH3F

Abstract Infrared-microwave two-photon spectra have been obtained for the ν3 bands of 12CH3F and 13CH3F with a two-photon spectrometer employing a CO2 laser and a computer-coupled microwave source operating in the 8–18 GHz region. Even though the intensities of the spectra for the double parity levels in these molecules are inversely proportional to the square of the microwave frequency, transitions have been observed with microwave frequencies of up to 16 GHz. Comparison of these observed two-photon frequencies to frequencies predicted from infrared laser Stark spectroscopy, and to frequencies calculated from vibration-rotation parameters obtained by fitting these and other frequencies, shows agreement to within a few MHz. Spectroscopic parameters for the ground and ν3 excited states of the two species are reported.

Study of the ν3 and 2ν3 ← ν3 bands of 12CH3F by infrared laser sideband and submillimeter-wave spectroscopy

Abstract An infrared laser sideband spectrometer operating in the CO 2 laser region with 8- to 18-GHz sidebands has been used to record 266 transitions in the ν 3 band and 84 transitions in the 2 ν 3 ← ν 3 band of 12 CH 3 F. The accuracy of the measured frequencies is estimated to be 1–3 MHz. A millimeter/submillimeter-wave spectrometer has been used to record the spectra of 48 pure rotational transitions in the ground vibrational state and 55 transitions in the v 3 = 1 vibrational state with an accuracy of 20–90 kHz. The new measurements have been combined with previous radio frequency and infrared laser results to derive sets of constants for the ground, v 3 = 1, and v 3 = 2 states for this molecule. Tables of the vibrational dependence of the parameters and of the near coincidences of the ν 3 and 2 ν 3 ← ν 3 band transitions with CO 2 laser frequencies are given.

The microwave spectrum, barrier to internal rotation, and dipole moment of cyclopropyl methyl ketone☆☆☆

^{*}

Matrix elements of some products of direction cosines and second-order quadrupole coupling calculations

This work was supported by the National Science Foundation.