ИСТИНА

The method of direct (Doppler&Sisyphus) molecular cooling (DMC) with lasers has recently attracted the increasing attention from the spectroscopic community. Particularly, considerable progress was achieved for cooling and trapping of the diatomic molecules in magneto-optical traps1 . One of the very attractive features of DMC is that such a technique can also be applied to polyatomic species2,3. As the numbers of polyatomic species (and their fragments obtained by e.g. photodissociation) is effectively infinite, the DMC method can be in principle considered as a candidate for universal method of obtaining the arbitrary cold samples. To prove the universality of DMC method that would be highly desirable to demonstrate a multitude of examples of molecules having diverse chemical and/or spectroscopic properties and at the same time amenable for direct laser cooling. In such a context considerable interest present closed shell polyatomic molecules which can be routinely obtained in gas phase or in molecular beams. In our previous article2 we outlined the scheme for identifying the polyatomic molecules with one (valence) electron over the closed shells, which molecules are expected to possess quasi-closed cooling transitions allowing efficient photon cycling and thus consequent Doppler&Sisyphus cooling. This takes place when valence electron undergoes transition between (mainly) non-bonding orbitals upon electronic excitation. For closed-shell molecules situation is expected to be more complicated. Nevertheless, there exist some classes of large closed-shell polyatomic molecules possessing rigid structure, which are weakly influenced by charge rearrangement in valence region. In our report we discuss the molecule 4a-aza-4b-boraphenanthrene4 as an example of such molecule and outline possible principles for identifying other closed-shell molecules possessing quasi-closed optical transitions.