Complex energies and the polyelectronic Stark problem: II. The Li n=4 levels for weak and strong fields

Themelis, SI; Nicolaides, CA

dc.contributor.author	Themelis, SI	en
dc.contributor.author	Nicolaides, CA	en
dc.date.accessioned	2014-03-01T01:51:02Z
dc.date.available	2014-03-01T01:51:02Z
dc.date.issued	2001	en
dc.identifier.issn	0953-4075	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/26225
dc.subject.classification	Optics	en
dc.subject.classification	Physics, Atomic, Molecular & Chemical	en
dc.subject.other	INDUCED TUNNELING RATES	en
dc.subject.other	H RESONANCE-SPECTRUM	en
dc.subject.other	AUTO-IONIZING STATES	en
dc.subject.other	MAGNETIC-FIELD	en
dc.subject.other	EXCITED-STATES	en
dc.subject.other	THEORETICAL RESOLUTION	en
dc.subject.other	MULTIPHOTON IONIZATION	en
dc.subject.other	ELECTRIC-FIELD	en
dc.subject.other	HYDROGEN-ATOM	en
dc.subject.other	1S(2)2S S-2	en
dc.title	Complex energies and the polyelectronic Stark problem: II. The Li n=4 levels for weak and strong fields	en
heal.type	journalArticle	en
heal.language	English	en
heal.publicationDate	2001	en
heal.abstract	We computed nonperturbatively, via the state-specific matrix complex eigenvalue Schrodinger equation (CESE) theory, the energy shifts and widths of all ten Li n = 4 levels which are produced by electric fields of strength, F, in the range 0.0-0.0012 au (6.17 x 10(6) V cm(-1)). By establishing the nature of the state vector to which every physically relevant complex eigenvalue corresponds, we delineated the field strength region where it is possible to characterize the perturbed levels in terms of small superpositions of unperturbed Li states (called here the weak field region) from the region where the mixing of the discrete and the continuous states renders such an identification impossible (the strong field region). For both regions, systematic and accurate CESE calculations have produced a complete adiabatic spectrum of perturbed energies. It turns out that the behaviour of the energies of the m = +/-1, +/-2 and +/-3 levels is smooth. In contrast, the Stark spectrum of the m = 0 levels contains not only all the n = 4 levels but also parts of the n = 3 and 5 manifolds, and is characterized by regions of crossing as well as of avoided crossing of the real part of the complex energies as a function of F. In the former case, the widths of the crossing (diabatic) levels differ considerably-even by two orders of magnitude. In the latter case, there are abrupt changes in the widths, a result of significant changes in the perturbed wavefunctions. For weak fields, which, for example, for the in = 0, n = 4 levels correspond to values up to about 2 x 10(-4) au, the one-electron semiclassical Ammosov, Delone and Krainov (ADK) formula for the widths produces reasonable trends. However, when the wavefunction mixing increases with field strength, it fails completely. For the four m = 0 levels, comparison is made with the results of Sahoo and Ho, obtained nonperturbatively by applying the complex absorbing potential (CAP) method. For a range of relatively weak fields, the CAP results for the widths do not follow a physically meaningful curve and deviate from our CESE results by orders of magnitude. As regards the energy spectrum, the one given by Sahoo and Ho for strengths up to 0.0005 au and the one given by us are substantially different, the former presenting a simple picture, without any avoided crossings. Given these differences, we take the opportunity to comment, via exemplars, on problems and solutions pertaining to the calculation of resonance states of polyelectronic atoms and molecules in terms of non-Hermitian approaches employing square-integrable function spaces.	en
heal.publisher	IOP PUBLISHING LTD	en
heal.journalName	JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS	en
dc.identifier.isi	ISI:000170637800016	en
dc.identifier.volume	34	en
dc.identifier.issue	14	en
dc.identifier.spage	2905	en
dc.identifier.epage	2925	en