J. W. C. Johns

Laser magnetic resonance spectroscopy of the ν2 fundamental band of HCO at 9.25 μm

The ν2 bending fundamental (ν0=1080.76 cm−1) of the formyl radical, HCO, has been studied using CO2 laser magnetic resonance. Fluorine atoms from a discharge in CF4 were reacted with H2CO to form the short‐lived HCO, which then flowed through an absorption cell located between the pole faces of an electromagnet and within the optical cavity of a CO2 laser. By means of the Zeeman effect, HCO, vibration‐rotation transitions were tuned through resonance with the laser lines. Numerous resonances involving levels with 1⩽N⩽7 and 1⩽Ka⩽3 were assigned, and from analysis of the spectra accurate determinations of the band origin, rotational, centrifugal distortion, spin‐rotation, and Fermi interaction parameters for ν2 were made. Fairly large changes in the values of A, ΔK, eaa, and ηaaaa between the ground and v2=1 vibrational states were observed.

The bending vibrational levels in C2D2 (X̃ 1Σ+g)

Improved sets of data have been recorded and analyzed in order to study the bending rovibrational energy levels of C2D2, in the regions of the ν5–ν4 difference band (FIR) and of the ν5 fundamental band (IR). A matrix model is setup to deal with a Darling–Dennison coupling between sets of bending levels as well as with the usual l‐type resonances. A simultaneous fit of the new data together with earlier microwave measurements produces an extended set of very accurate parameters, including for the first time in C2D2 s45 and qkt.

High resolution and the accurate measurement of intensities

Absolute intensities in several vibration rotation bands of CO2 and in the pure rotation spectrum of CO have been measured. The results have been used to assess the precision and accuracy which such measurements can attain when made with a high resolution Fourier transform spectrometer.

Stark spectroscopy with the CO laser: The dipole moment of H2CO in the v2=2 state

Some transitions of the 2ν2←ν2 hot band of H2CO near 5.8 μm have been observed by the laser Stark technique using a 20 cm long intracavity absorption cell with about 4 mtorr total pressure at room temperature. The detection of this weak hot band (partial pressure in the v2=1 state ?8×10−7 torr) illustrates the high sensitivity of intracavity laser absorption spectroscipy. From the measured resonant fields of the transitions, the dipole moment of H2CO in the v2=2 state has been determined. The use of phase sensitive detection at twice the Stark modulation frequency is illustrated; this 2f detection effectively measures the strength of the transient nutation signal in the absorbing gas, and in some cases results in a better signal to noise ratio than does conventional 1f detection.

The spectrum of CH3OH between 200 and 350 cm−1: Torsional transitions and evidence for state mixings

Abstract In the framework of our systematic investigation of the infrared and far infrared spectrum of CH3OH by high-resolution Fourier transform spectroscopy, we present a catalog of 8800 absorption lines between 200 and 352 cm−1. The Taylor expansion coefficients for evaluating the energies of the levels involved in the transitions are also given. All of the lines occurring in the 200–352 cm−1 region correspond to transitions between torsionally excited states. Some forbidden lines (Δn ≠ 0; ΔK = 0), indicating state mixings, have been found.

The D2Π−X2Σ+ Band System of CaH

The D2Σ+-X2Σ+ band system of CaH has been reinvestigated in emission and in absorption. Analysis shows that the previously accepted vibrational numbering must be changed with the result that the vibration frequency of the D state must be reduced by a factor of two. Anomalies in the rotational structure of the D state are explained by a strong homogeneous interaction with excited vibrational levels of B2Σ+.

Analysis of CH 3 OH far infrared laser lines optically pumped by sequence band and isotopic CO 2 lasers

Assignments are presented for seven far infrared (FIR) laser lines of CH 3 OH pumped by the S-9P(31),18-10R(24),13-9R(26) , and 13-9P(16) CO 2 laser lines, plus an interesting speculation for the FIR line pumped by the 18-9P(12) CO 2 line. Frequencies have been deduced to a substantially improved accuracy of ±0.001 cm-1from IR and FIR spectroscopic combination differences for most of the assigned lines as well as three other predicted transitions. In addition, accurate frequencies are given for 13 predicted FIR laser transitions which are expected from the IR spectrum to be pumped by three16O12C18O laser lines.

Fourier transform spectroscopy of SrH: The A-X and B-X band systems

The absorption spectrum of SrH in the region 6800-7600 A has been investigated by Fourier transform spectroscopy. A new calculation of the ground state molecular constants and a deperturbation of the A2Π/B2Σ+ interaction has been performed. Molecular constants of the deperturbed states are given.

Fourier Transform Spectroscopy of the B2Σ-X2Σ Transition of BaH

The B2Σ-X2Σ band system of gaseous barium hydride in the wave length region 8900-11200 A has been examined in absorption using a King furnace. The spectrum has been obtained by means of Fourier transform spectroscopy. Seven bands have been rotationally analyzed. Term values and molecular constants of the B2Σ and X2Σ states have been determined by standard least-squares analysis. The following molecular constants have been derived (cm-1): Te ωe ωexe ωeye Be αe 104 × De B2Σ+ 11092.593 1088.898 15.471 0.0237 3.26879 0.07061 1.1585 X2Σ+ 0. 1168.433 14.611 0.0276 3.38226 0.06568 1.1234

Laser-Stark and Fourier-transform spectroscopy of the ν 3 band of monodeuterated formic acid, HCOOD

The ν3 fundamental band of monodeuterated formic acid, HCOOD, at 5.64 μm has been studied by using a combination of CO-laser-Stark spectroscopy and high-resolution Fourier-transform spectroscopy. The analysis of the Fourier-transform data, together with all previous pure rotational ground-state data, gave precise values for the ν3-band origin and rotational and centrifugal distortion parameters. Slightly refined ground-state parameters were also obtained. A c-type Coriolis interaction between ν3 and ν6 + ν7 was included in the analysis, resulting in a value for the interaction parameter and for some effective parameters of the perturbing state. A second weaker Coriolis interaction between ν3 and ν5 + ν9 was noted but not analyzed. The Stark data yielded precise values for the μa and μb dipole-moment components in the ground and excited states.