Experimental 2CH excitation in acetylene-containing van der Waals complexes

Assignment of the methanol OH-stretch overtone spectrum using the pattern recognition method

We present the measurement and analysis of the 2OH stretching band of methanol between 7165 cm-1 and 7230 cm-1 cooled down to 26 ± 12 K in a buffer gas cooling experiment. Measurements were performed with a cavity ring-down spectrometer having a detection limit αmin = 2 × 10-10 cm-1. A total of 350 rovibrational transitions were assigned and 62 rovibrational transitions were tentatively assigned. This assignment was performed using the pattern recognition method developed by Rakvoský et al. [Phys. Chem. Chem. Phys., 2021, 23, 20193-20200]. In this work, we extended their method by using information on the relative intensities of the transitions to add one criterion to the validation of the assignments, allowing us to firmly assign 188 additional rovibrational transitions and to tentatively assign 14 more compared to the ir work.

Unusual Dynamics and Vibrational Fingerprints of van der Waals Dimers Formed by Linear Molecules and Rare-Gas Atoms

Detailed structural, dynamical, and vibrational analyses have been performed for systems composed of linear triatomic molecules solvated by a single rare-gas atom, He, Ne, or Ar. Among the chromophores of these van der Waals (vdW) dimers, there are four neutral molecules (CO2, CS2, N2O, and OCS) and six molecular cations (HHe2+, HNe2+, HAr2+, HHeNe+, HHeAr+, and HNeAr+), both of apolar and polar nature. Following the exploration of bonding preferences, high-level four-dimensional (4D) potential energy surfaces (PESs) have been developed for 24 vdW dimers, keeping the two intramonomer bond lengths fixed. For these 24 complexes, over 1500 bound vibrational states have been obtained via quasi-variational nuclear-motion computations, employing exact kinetic-energy operators together with the accurate 4D PESs and their 2D/3D cuts. The reduced-dimensional (2D to 4D) dimer models have been compared with full-dimensional (6D) ones in the cases of the neutral CO2·Ar and charged HHe2+·He dimers, corroborating the high accuracy of the 2D to 4D vibrational energies. The reduced-dimensional models suggest that (a) while the equilibrium structures are T-shaped and planar, the effective ground-state structures are nonplanar, (b) certain bound states belong to collinear molecular structures, even when they are not minima, (c) the vdW vibrations are heavily mixed and many states have amplitudes corresponding to both the T-shaped and collinear structures, (d) there are a few dimers, for which even some of the vdW fundamentals lie above the first dissociation limit, and (e) the vdW vibrations are almost fully decoupled from the intramonomer bending motion.

Experimental and theoretical investigations of H2O-Ar

We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H₂O-Ar in the 2OH excitation range of H₂O. 24 sub-bands have been observed. Their rotational structure (T_rot = 12 K) is analyzed and the lines are fitted separately for ortho and para species together with microwave and far infrared data from the literature, with a unitless standard deviation σ=0.98 and 1.31, respectively. Their vibrational analysis is supported by a theoretical input based on an intramolecular potential energy surface obtained through ab initio calculations and computation of the rotational energy of sub-states of the complex with the water monomer in excited vibrational states up to the first hexad. For the ground and (010) vibrational states, the theoretical results agree well with experimental energies and rotational constants in the literature. For the excited vibrational states of the first hexad, they guided the assignment of the observed sub-bands. The upper state vibrational predissociation lifetime is estimated to be 3 ns from observed spectral linewidths.

Alcohol dimers – how much diagonal OH anharmonicity?

The massive infrared attenuation and increased anharmonicity of OH stretching overtones in alcohol dimers is experimentally quantified.

Note: A very simple circuit for piezo actuator pseudo-tracking for continuous-wave cavity ring-down spectroscopy

A very simple circuit for pseudo-tracking of the piezo actuator for continuous-wave cavity ring-down spectroscopy (cw-CRDS) is presented. The circuit is based on an ordinary positive-edge trigger D-type flip flop integrated circuit, has a low parts count, and can be easily assembled using only off the shelf components. The circuit can be straightforwardly incorporated into most cw-CRDS setups and, thanks to the increased ring-down event rate, higher sensitivity or lower data acquisition time can be achieved.