Infrared-microwave Double Resonance Research Articles

Infrared—microwave double resonance in NH 3: Studies of collision-induced transitions in the presence of a high field stark effect

Several infrared—microwave double resonance experiments are described in ammonia in the presence of a high field Stark effect. The dipolar type selection rules for collision-induced transitions are confirmed and the advantages of the Stark method are discussed.

Collisional relaxation among rotational levels of NH 3 studied by infrared-microwave double resonance

Double-resonance signals induced by molecular collisions are observed in 25 inversion transitions of NH 3. It is found that the collision-induced transitions do not necessarily occur in accordance with the dipole-type selection rule reported previously.

Infrared-Microwave Double Resonance Experiments with NH3

Infrared-microwave double resonance experiments have been performed with ammonia. The experimental equipment consists of a microwave spectrometer and an N2O-laser. First results are in general agreement with previous experiments of other authors. Higher resolution reveals more details of the IR-pumped ν2[aqQ(8, 7)] transition. Several four-level systems were observed.

Direct observation of rotational energy transfer in ammonia by time-resolved infrared—microwave double resonance

An N 2O laser is used to pump the ground vibrational state (8,7) inversion doublet of 14NH 3 while simultaneously monitoring other ground state doublets. Time-resolved rotational energy transfer signals are observed in accordance with known selection values. Absolute rates of rotational energy transfer processes are estimated.

Time-resolved infrared-microwave double resonance in 13CH3F: Theory and experiment

Infrared-microwave double resonance experiments on 13CH3F are described which lead to a direct measurement of T1, the relaxation time due to population differences for the two transitions J = 3 → J = 4; K = 3 and J = 4 → J = 5; K = 3 in the ground vibrational state. We find T1 = (10.5 ± 0.6) μsec mtorr. Comparing this work with low-power linewidth measurements which measure T2, the relaxation time of the induced polarization, indicates that T1 = T2 for the above two transitions. The theory used to interpret the experiments is developed starting from the density matrix formalism which leads to the electric dipole analog of the Bloch equations in nuclear magnetic resonance. The equations are solved for the conditions appropriate to this experiment which gives the results involving T1 and T2. The theory developed here should be of use in interpreting time-resolved infrared-microwave experiments in the future.

Rotational Transitions of CH4 in the v3=1 Excited State Observed by an Infrared-Microwave Double Resonance Method

Rotational Transitions of CH4 in the v3=1 Excited State Observed by an Infrared-Microwave Double Resonance Method

Microwave Spectroscopy of the Vibrationally Excited State of Molecules by Infrared-Microwave Double Resonance

Microwave Spectroscopy of the Vibrationally Excited State of Molecules by Infrared-Microwave Double Resonance

Infrared-microwave double resonance of NH3 in the presence of a high-field Stark effect

Exact coincidences between infrared vibration-rotation transitions of NH3 and CO2 or N2O laser lines have been obtained using high-field Stark effect. Different schemes of pumping have been used, giving either increase or decrease of microwave absorption.

Infrared-Microwave Double Resonance in H2CO with a Zeeman-Tuned 3.5µm He-Xe Laser

Infrared-microwave double resonance effects in formaldehyde are observed by using a method of microwave pumping and infrared detection. The pressure dependence of the double resonance signal is observed with the gas cell either inside or outside of the laser cavity. The signal is observed to change its sign at a low pressure of formaldehyde. A rate-equation approach is used to calculate the pressure dependence of the double resonance signal. The observed change in sign is explained by higher-order effects of double resonance. A good agreement between the theoretical and the observed results is obtained. The double resonance effects on the inverted Lamb dip of the infrared absorption of formaldehyde are also observed. The dip splits into a doublet when the strong resonant microwave is applied.

Transient-Nutation Effects in Time-Resolved Infrared-Microwave Double Resonance of Ammonia

Transient nutation is observed in the time-resolved infrared-microwave double resonance of ammonia. This behavior is described by a Bloch equation for relaxation of the ammonia inversion levels, with an effective ${T}_{2}$ cross section of 400 \ifmmode\pm\else\textpm\fi{} 50 ${\mathrm{\AA{}}}^{2}$. A similar effect was produced by rapidly switching the Stark field applied to the molecules, which suddenly brings them into resonance with the cw microwave radiation.

Infrared-microwave double resonance in molecules

Infrared-microwave double resonance in molecules

Pressure dependence of infrared-microwave double resonance in formaldehyde

The double resonance in three levels of H 2CO is observed with the 3.5 μm He-Xe laser and millimetre waves. At low pressures below several mtorr the double resonance signals are inverted. The observed pressure dependence is explained satisfactorily by a rate-equation approach including higher-order effects of two radiations.

Infrared-Microwave Double Resonance of NH3 Using an N2O Laser

Infrared-Microwave Double Resonance of NH3 Using an N2O Laser