Photoabsorption spectrum of helium trimer cation—Theoretical modeling

Abstract

The photoabsorption spectrum of He3(+) is calculated for two semiempirical models of intracluster interactions and compared with available experimental data reported in the middle UV range [H. Haberland and B. von Issendorff, J. Chem. Phys. 102, 8773 (1995)]. Nuclear delocalization effects are investigated via several approaches comprising quantum samplings using either exact or approximate (harmonic) nuclear wavefunctions, as well as classical samplings based on the Monte Carlo methodology. Good agreement with the experiment is achieved for the model by Knowles et al., [Mol. Phys. 85, 243 (1995); Mol. Phys. 87, 827 (1996)] whereas the model by Calvo et al., [J. Chem. Phys. 135, 124308 (2011)] exhibits non-negligible deviations from the experiment. Predictions of far UV absorption spectrum of He3(+), for which no experimental data are presently available, are reported for both models and compared to each other as well as to the photoabsorption spectrum of He2(+). A simple semiempirical point-charge approximation for calculating transition probabilities is shown to perform well for He3(+).

Size Evolution of Photoabsorption Spectra of Small Clusters: A Computational Study

“…Importantly, an almost perfect agreement was found between ab initio and semi-empirical DIM/PCA results in the case of the two smaller cluster sizes (He þ 3 and He þ 4 ). This finding was fully in line with another study [8] where an R/2 dependence of the TDM was obtained for He þ 2 from similarly accurate ab initio calculations (icMRCI/aug-cc-pVQZ). Even for larger cluster sizes (represented by He þ 10 in Ref.…”

“…The most important conclusion one can draw from this figure is that the photoabsorption spectra of $${{\rm{He}}_3^ + }$$ , $${{\rm{He}}_4^ + }$$ , and $${{\rm{He}}_{10}^ + }$$ recorded experimentally in the mid‐UV region are, apart from slightly different heights, very similar to one another. Since a well pronounced absorption band located in the mid‐UV region is a strong marker of a triatomic chromophore of the absorbing complex (i. e., a chromophore consisting of three atoms on which the positive charge has condensed), [8] we may speak about this type of spectra as about trimer‐like spectra.…”

“…An ideal, though indirect marker of the evolution of the ionic core with cluster size is the cluster photoabsorption spectrum since the ionic core acts as an efficient chromophore. Despite this, however, just a couple of experimental [7] and theoretical [8–10] studies of $${{{\rm H}{\rm e}}_{N}^{+}}$$ photoabsorption have been published up to now.…”

“…No systematic investigation of how $${{{\rm H}{\rm e}}_{N}^{+}}$$ photoabsorption spectra evolve with the cluster size was performed. In the present work, we partly fill this gap by systematically investigating the evolution of the $${{{\rm H}{\rm e}}_{N}^{+}}$$ photoabsorption spectra over the missing range of cluster sizes ( N =5–9) with the main goal to obtain a comprehensive picture of the $${{{\rm H}{\rm e}}_{N}^{+}}$$ interaction with electromagnetic radiation for N ranging between N =3 (or even [8] N =2) and N =10.…”

Non-adiabatic dynamics combining Ehrenfest, decoherence, and multiscale approaches applied to ionic rare-gas clusters photodissociation, post-ionization fragmentation, and collisions

“…Following semiclassical ideas and assuming purely vertical transitions, an histogram is built and according to the potential energy difference the transition probability is accumulated from some appropriate sampling of nuclear configurations in the ground state [26,27]. This sampling may employ classical trajectories calculated under microcanonical conditions (fixed energy) [18], but care should be taken with the ergodicity [26,27,51], or under canonical conditions (fixed temperature) [43], often using Monte Carlo procedures, or from importance sampling of quantum wave functions either coming from a normal mode approach [52], a full quantum calculation [53], or from a quantum Monte Carlo evaluation [54]. In Fig.…”