High-resolution rovibrational and rotational spectroscopy of the singly deuterated cyclopropenyl cation, c-C3H2D.

Applying a novel action spectroscopic technique in a 4 K cryogenic ion-trap instrument, the molecule c-C3H2D+ has been investigated by high-resolution rovibrational and pure rotational spectroscopy for the first time. In total, 126 rovibrational transitions within the fundamental band of the ν1 symmetric C-H stretch were measured with a band origin centred at 3168.565 cm-1, which were used to predict pure rotational transition frequencies in the ground vibrational state. Based on these predictions, 16 rotational transitions were observed between 90 and 230 GHz by using a double-resonance scheme. These new measurements will enable the first radio-astronomical search for c-C3H2D+.

Rovibrational spectroscopy of the CH+-He and CH+-He4 complexes.

A cryogenic 22-pole ion trap apparatus is used in combination with a table-top pulsed IR source to probe weakly bound CH+-He and CH+-He4 complexes by predissociation spectroscopy at 4 K. The infrared photodissociation spectra of the C-H stretching vibrations are recorded in the range of 2720-2800 cm-1. The spectrum of CH+-He exhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm-1, and thus confirms it to have a T-shaped structure. For CH+-He4, the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.

High-resolution infrared action spectroscopy of the fundamental vibrational band of CN.

Rotational-vibrational transitions of the fundamental vibrational modes of the 12C14N+ and 12C15N+ cations have been observed for the first time using a cryogenic ion trap apparatus with an action spectroscopy scheme. The lines P(3) to R(3) of 12C14N+ and R(1) to R(3) of 12C15N+ have been measured, limited by the trap temperature of approximately 4 K and the restricted tuning range of the infrared laser. Spectroscopic parameters are presented for both isotopologues, with band origins at 2000.7587(1) and 1970.321(1) cm-1, respectively, as well as an isotope independent fit combining the new and the literature data.

Accurate Rotational Rest Frequencies for Ammonium Ion Isotopologues.

We report rest frequencies for rotational transitions of the deuterated ammonium isotopologues NH3D+, NH 2 D 2 + and NHD D 3 + , measured in a cryogenic ion trap machine. For the symmetric tops NH3D+ and NHD 3 + one and three transitions are detected, respectively, and five transitions are detected for the asymmetric top NH 2 D 2 + . While the lowest frequency transition of NH3D+ was already known in the laboratory and space, this work enables the future radio astronomical detection of the two other isotopologues.

First Laboratory Detection of Vibration-Rotation Transitions of 12CH+ and 13CH+ and Improved Measurement of their Rotational Transition Frequencies.

The long-searched C-H stretches of the fundamental ions CH+ and 13CH+ have been observed for the first time in the laboratory. For this, the state-dependent attachment of He atoms to these ions at cryogenic temperatures has been exploited to obtain high-resolution rovibrational data. In addition, the lowest rotational transitions of CH+, 13CH+ and CD+ have been revisited and their rest frequency values improved substantially.

Accurate Frequency Determination of Vibration-Rotation and Rotational Transitions of SiH.

The fundamental 28SiH+ ion has been characterized in a collaborative work, utilizing a hollow-cathode-discharge laser-spectrometer and a cryogenic ion trap spectrometer. Twenty-three vibration-rotation transitions around 4.75 µm have been detected with high accuracy. This has facilitated the first direct measurement of the pure rotational transition J = 1 ← 0 at 453056.3632(4) MHz in the trap spectrometer. The measured and accurately predicted transitions enable the search for this ion in space with IR and sub-mm telescopes.

Direct determination of state-to-state rotational energy transfer rate constants via a Raman-Raman double resonance technique: ortho-acetylene in v(2)=1 at 155 K.

A new technique for the direct determination of state-to-state rotational energy transfer rate constants in the gas phase is presented. It is based on two sequential stimulated Raman processes: the first one prepares the sample in a single rotational state of an excited vibrational level, and the second one, using the high resolution quasi-continuous stimulated Raman-loss technique, monitors the transfer of population to other rotational states of the same vibrational level as a function of the delay between the pump and the probe stages. The technique is applied to the odd-J rotational states of v(2)=1 acetylene at 155 K. The experimental layout, data acquisition, retrieval procedures, and numerical treatment are described. The quantity and quality of the data are high enough to allow a direct determination of the state-to-state rate constant matrix from a fit of the experimental data, with the only conditions of detailed balance and of a closed number of states. The matrix obtained from this direct fit is also compared with those obtained using some common fitting and scaling laws.