Laser induced fluorescence of Mg-phthalocyanine in He droplets: Evidence for fluxionality of large H2 clusters at 0.38K

Abstract

The formation of Ar and H2 clusters, having up to 900 particles in helium droplets, has been studied via laser induced fluorescence of attached Mg-phthalocyanine (Mg-Pc) molecules. In the experiments, one Mg-Pc molecule in average was added to each He droplet either before or after the cluster species, and the shift of the spectrum of the Mg-Pc molecules was studied as a function of the cluster size. For Ar clusters, about a factor of 2 smaller matrix shift was observed for the late pickup of the Mg-Pc molecules as compared with the prior pickup, indicating that in the former case, the Mg-Pc molecules reside on the surface of the preformed Ar clusters. On the other hand, the spectra of the Mg-Pc molecules attached to H2 clusters are independent of the pickup order, which is consistent with Mg-Pc molecules residing near the center of the H2 clusters in both cases. Therefore H2 clusters remain fluxional in helium droplets at T=0.38 K. No significant differences in the spectra were observed between the para-H2 and ortho-H2 clusters.

Evolution of dopant-induced helium nanoplasmas

“…By leaking into the cell a controlled amount of krypton (Kr) or xenon (Xe) rare gas using a dosing valve (leak rate <10 −10 mbar l s −1 ) the mean number of dopants per nanodroplet K can be adjusted. Taking into account the shrinkage of He droplets due to evaporation of He atoms induced by the pick-up and cluster aggregation process, K can be determined from the cell pressure and the droplet size according to modified Poissonian pick-up statistics [20]. This model is validated using Monte-Carlo simulations of the pick-up process as detailed in [21].…”

Spectroscopy of 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) attached to rare gas samples: Clusters vs. bulk matrices. I. Absorption spectroscopy

“…13 Only the co-expansion of helium and hydrogen with less than 1% hydrogen 13 or the aggregation mechanism of somewhat smaller hydrogen clusters in helium droplets have shown liquid-like properties. 14,15 Large rare gas clusters have been shown to provide an ideal support for chemical reactions and catalysis due to the confinement of the reactants to the clusters' surface and the corresponding high reaction probabilities. 16 Correspondingly, single atoms as well as di-and tri-atomic molecules and a few larger molecules (e.g., SiF 4 , SF 6 ) have been attached to large argon clusters.…”

Ro‐vibrational Spectra of (para‐H2)N‐CH4 in He Droplets

“…[21][22][23] The first observation of microscopic superfluidity in H 2 was reported by Grebeneve tal. [30] For (H 2 ) N -N 2 O, [29] am onotonic decrease in the rotational constant up to N = 13 was observed indicating no evidenceo fs uperfluid behavior.R ecently,s pectra of larger molecules, such as Mgphthalocyanine and tetracene with up to about 1000 hydrogen molecules, have been studied in helium droplets, indicating af luxional behavior of large hydrogen clusters at T = 0.38 K. [33,34] In this work we extend the investigation of hydrogen clusters to ah ighly symmetric chromophorem olecule, namely CH 4 .T he spectra of single CH 4 moleculesa nd clusters in He droplets have been reported. [26] Since then, high-resolution infrared spectra have been reported for an umber of molecules, such as HF, [27][28] N 2 O, [29] HCN, [30] CO, [31] and CO 2 [32] with varied numbers of p-H 2 molecules attached.…”

“…However,t he rotation was hindered upon completion of the first solvation shell at N = 14. [30] For (H 2 ) N -N 2 O, [29] am onotonic decrease in the rotational constant up to N = 13 was observed indicating no evidenceo fs uperfluid behavior.R ecently,s pectra of larger molecules, such as Mgphthalocyanine and tetracene with up to about 1000 hydrogen molecules, have been studied in helium droplets, indicating af luxional behavior of large hydrogen clusters at T = 0.38 K. [33,34] In this work we extend the investigation of hydrogen clusters to ah ighly symmetric chromophorem olecule, namely CH 4 .T he spectra of single CH 4 moleculesa nd clusters in He droplets have been reported. [35][36][37][38] In this work clusters of up to 80 p-H 2 molecules with CH 4 have been assembled inside He droplets and studied via infrared spectroscopy of the u 3 band…”