A newly developed IR sub-Doppler technique is introduced. First applications of this technique to the radical NO and the molecular ion DBr+ are presented. For NO a resolution of 3 MHz at 1900 cm-1 (stretching fundamental IR absorption) is achieved. Power and pressure broadening can be observed. In higher magnetic fields the resolution is shown to be limited by the inhomogeneity of the magnetic field. The spectrum of DBr+ is the first IR Lamb dip spectrum of a molecular ion to be reported. The transitions are partially saturated (S ≪ 1) and the effective linewidth is estimated to be between 5 and 10 MHz. The DBr+ ions are generated in an anomalous discharge confined by a magnetic field. The influence of the ambipolar diffusion is found to be negligible.

We have achieved cw-laser emission from a liquid nitrogen cooled CO plasma on overtone bands Δv=2. 150 rotational lines of the v = 16 → 14 to v = 37 → 35 vibrational bands have been observed so far covering the special range from 2.86 to 4.07 μm. The maximum single line power exceeds 50 mW.

We present the first spectroscopic observation of the nickel-hydride free radical in the infrared region in the gas phase. A set of vibrational rotational molecular constants for the electronic ground state is given.

By employing CO Laser Faraday L.M.R. using a combination of concentration modulation and magnetic field modulation the vib-rot spectrum of the first excited state of CO: a 3π has been observed. Altogether 50 transitions (214 Zeeman components) for v=1←0 to v=3←2 within all fine structure systems of the a 3π state have been assigned. They were fitted to a hamiltonian, where the interaction between the a 3π and the a′ 3Σ state is taken into account only by perturbation theory. Our set of parameters describes the experimental data within 10−3 cm−1, which is better than any other I.R.-data available so far.

A double modulation technique was developed for selective detection of open shell molecular ions. By employing this technique the vibration-rotation spectrum of DBr+ in its X 2Π3/2 ground state has been recorded. A new set of vibration-rotation molecular constants for both isotopic species D79Br+ and D81Br+ is given.

Transitions between Rydberg states of atomic chlorine have been detected between 1477 and 1507 cm-1 by the technique of carbon monoxide laser magnetic resonance (LMR). Transitions have been observed in both emission and absorption. The spectra have been assigned for those transitions involving levels which have been identified previously. However, several more resonances are unassigned, revealing the presence of previously unidentified states of atomic chlorine. Many of the lines show resolved nuclear hyperfine structure.

Infrared laser spectroscopy of open shell molecules can take advantage of the Zeeman effect for both modulating and tuning of the corresponding transitions into resonance with a fixed frequency laser line. Thus it is very similar to EPR, however the tuning range is much smaller than the transition frequency, which can be either the rotational or the vibrational energy of a molecule. This method, which is well known as “Laser Magnetic Resonance” (LMR), has first been developed and brought to perfection by K.M. EVENSON and coworkers /l/. They achieved sensitivies down to 10 diatomic molecules per cm in the far infrared region for pure rotational molecular transitions. An essential feature of EVENSON’s LMR system is the intracavity arrangement, i.e. the absorption cell, where the shortlived species are generated by a chemical reaction, is incorporated in the laser cavity. The high sensitivity of this intracavity setup can be understood in terms of the increased effective pathlength through the sample and the non- linearity of the laser system, as has been pointed by H.E.RADFORD et al. /2/.

We report rotationally resolved vibrational spectra of the DCL+ molecular ion for ν = 1 ← 0 to ν = 7 ← 6 with a Faraday-L.M.R. spectrometer. The ions were generated in a d.c.-excited discharge of the anomalous type near 2 torr total pressure. A small probe modulation coil allows spatial resolution of the concentration profile along the discharge. Comparisons of such profiles between anomalous and normal discharge conditions are presented. Spectroscopic constants for DCl+ X 2Π3/2 are reported.

We describe a mid-infrared Laser Magnetic Resonance (LMR) spectrometer which is based on a cryomagnet and a sealed-off CO-laser. Faraday rotation combined with a multireflection cell is used for polarization sensitive detection of molecular radical ions. Experimental details and first spectroscopic examples are given.

By employing a mid-infrared laser magnetic resonance (L.M.R.)-spectrometer the fundamental vibrational rotational band of SD in its X 2Π3/2 ground state has been observed. The band origin ν0 = 1885·9114(2) cm-1 and the rotational constants B e = 4·95130(3) cm-1 and αe = 0·10308(1) cm-1 were determined.

Vibration-rotation transitions in the fundamental band of the radical ion DCl+ have been detected. Transitions of the two isotopic species D 35Cl+ and D 37Cl+ have been recorded up to J = 3·5 and the data have been fitted using the hamiltonian of Brown et al. [4].

Rotation of the linear polarization in a longitudinal (Faraday effect) and a transverse (Voigt effect) magnetic field can be used to increase the sensitivity of laser magnetic resonance spectrometers. Theoretical background and experimental results for these new techniques are presented. The sensitivity and content of information are discussed for the various LMR methods.

A mid infrared CO-Laser-Magnetic-Resonance spectrometer is introduced which employs polarisation perceptive detection schemes for sensitivity enhancement. Using the magnetic circular birefringence (Faraday effect) or the magnetic circular dichroism a detection limit of Iabs/I <10−7 has been achieved in an extracavity single pass setup with 30cm absorption length and without signal integration. The intracavity application of the polarization sensitive detection method resulted in an improvement of the signal-to-noise ratio by a factor of 30. The detection limit then attains the 10ppt level for NO. As the bending mode vibrational frequency of the hydroperoxyl radical is within the spectral range of the CO laser a detection of HO2 in ambient air may potentially be possible.