Infrared spectroscopy of the isomers of magnesium–HCN formed in helium nanodroplets: Comparisons with ab initio calculations

Abstract

High-resolution infrared spectra are reported for two isomers of the magnesium–HCN binary complex, corresponding to the magnesium bonding at the nitrogen and hydrogen ends of the molecule. Stark spectra are also reported for these complexes, from which the corresponding dipole moments are determined. Ab initio calculations confirm that the potential energy surface has two minima, consistent with the experimentally determined structures. The wave functions of the two dimensional intermolecular coupled cluster singles doubles (triples) potential energy surface, calculated with the collocation method, are also reported for the magnesium–HCN system and are used to calculate the vibrationally averaged dipole moment for both isomers, which are then compared to experiment.

Rotational Dynamics of HCN−M (M = Na, K, Rb, Cs) van der Waals Complexes Formed on the Surface of Helium Nanodroplets

“…6 In Figure 5, the smooth line is a simulated rigid linear rotor spectrum, using a rotational constant of B′′ ) 9.4 MHz, assuming a rotational temperature of 0.37 K. While a P and R branch linear rotor spectrum was anticipated, it was quite surprising to find that the moment of inertia of the rotational motion was 5.3 × 10 4 amu‚Å 2 . In Figure 6, the HCNNa spectrum is compared with the HCN-Mg spectrum, 50 Comparing the HCN-Na zero-field spectra shown in Figures 5 and 6, we find the rotational constant has apparently increased upon changing the average droplet size from 10 000 to 7200 helium atoms. While the shapes of rotational lines have been observed to be droplet size dependent, as a result of inhomogeneous broadening, there is no other example, to our knowledge, of a rotational constant that varies so dramatically with droplet size.…”

Superfluid Helium Droplets: A Uniquely Cold Nanomatrix for Molecules and Molecular Complexes

“…Homogeneous clusters which have been studied in the IR region include (SF 6 ) n [130,144] (n = 2-4), (HCCCN) 2 , [136] (CH 3 OH) n n = 2-5, [176] (CH 3 CN) n n = 2-6, [176] (HCN) n n = 2-7, [145,146] (HF) n n = 2-8, [177][178][179] and (H 2 O) n n = 2-6. [180][181][182] The number of heterogeneous van der Waals complexes studied is even larger and includes such systems as HCN-H 2 (parahydrogen (pH 2 ), ortho-hydrogen (oH 2 ), para-deuterium (pD 2 ), ortho-deuterium (oD 2 ), HD), [183,184] HCN-C 2 H 2 , [185] HCN-Mg n (n = 1-3), [152,186] HF-H 2 (pH 2 , oH 2 , pD 2 , oD 2 , HD), [187,188] and HF-Ar n (n = 1-6) (Ne,Kr), [189] and OCS-(H 2 ) n (n = 1-17). [148][149][150][151] In most of these systems rotational resolution has been achieved.…”

Spectroscopy and dynamics in helium nanodroplets

“…Helium nanodroplets are particularly suited for the study of molecules bound to small metal clusters grown inside the droplet. The Miller group has published several papers reporting the IR spectra of HCN [47,48,230], HCCCN [231], and HCCH [232] complexed with Mg atoms and small clusters. Strongly nonadditive shifts in the IR fundamental transition of the molecules are suggestive to changes in the bonding of the Mg clusters, particularly upon going from Mg 3 to Mg 4 [230].…”