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Oznaka: 0098033

ISTRAŽIVANJA KEMIJSKE REAKTIVNOSTI I FEMTOSEKUNDNIH PROCESA

INVESTIGATION ON CHEMICAL REACTIVITY AND ULTRAFAST PROCESSES

Voditelj projekta: dr. sc. Aleksandar Sabljić

Tel. ++385 1 456-1089   e-mail: [e-mail]

Suradnici
Nađa Došlić, doktorica fiz. znanosti, znanstvena suradnica
Goran Kovačević, dipl. ing. kemije, znanstveni novak u suradničkom zvanju asistenta
Ivan Ljubić, doktor kem. znanosti, znanstveni novak u suradničkom zvanju višeg asistenta
Ivana Matanović, dipl. ing. kemije, znanstvena novakinja u suradničkom zvanju asistentice
Aleksandar Sabljić, doktor kem. znanosti, znanstveni savjetnik

Tehnički suradnici
Biserka Špoljar, tehničarka

Vanjski suradnici
Sanja Sekušak, doktorica kem. znanosti, PLIVA d.d., Zagreb (konzultantica)

Program rada i rezultati na projektu:

Provedeno je detaljno ab initio CASSCF/CASPT2 istraživanje reakcijskog mehanizma adicije ozona na fluoreten u plinskoj fazi. Počevši od primarnog adicijskog produkta (primarni fluorozonid) istraženi su svi mogući konfiguracijski i konformacijski načini njegovog cijepanja u odgovarajući Criegee-ov međuprodukt i karbonilni spoj. Sve stacionarne točke na reakcijskoj plohi i pripadni harmonijski vibracijski valni brojevi izračunati su na CASSCF/cc-pVTZ razini teorije te su utočnjene na CASPT2/cc-pVTZ razini. 

Poliklorirani derivati dibenzo-p-dioksina zbog svoje postojanosti, globalne rasprostranjenosti te toksičnih, mutagenih, kancerogenih i teratogenih svojstava spadaju u skupinu najopasnijih poznatih zagađivala. S ciljem boljeg poznavanja njihovog ponašanja u okolišu te štetnog djelovanja na ljude istraživana su elektronska i geometrijska svojstva osnovnog i pobuđenih singletnih i tripletnih stanja dibenzo-p-dioksina CASSCF/CASPT2(g₂) pristupom uz primjenu cc pVDZ baznog seta te potpunog aktivnog prostora p-elektrona. Pored toga još uvijek nisu sa sigurnošću određene structure niti osnovnog niti pobuđenih elektronskih stanja. Izračunata geometrija i vibracijske frekvencije izvrsno se slažu s postojećim izmjerenim (IR, Raman i fosforescencijskim spektrima) i izračunatim podacima. Izračunate energije pobuđenih stanja su u puno boljem slaganju s eksperimentalnim podacima nego dosadašnji teorijski rezultati. Pokazano je da sva p-p* pobuđena stanja posjeduju planarnu geometriju te da ne dolazi do C_2v relaksacije pri prijelazu iz osnovnog u p p* pubuđena stanja iako postoji niskofrekventna vibracija mahanja benzenskih prstenova i u osnovnom S₀(¹A_g) i u prvom pobuđenom stanju S₁(¹B_2u). Izračunate oscilatorne snage su u izvrsnom slaganju s izmjerenim vrijednostima te potvrđuju da su 2¹B_2u ¬ 1¹A_g and 2¹B_1u ¬ 1¹A_g elektronski prijelazi najintenzivniji dok jedini dozvoljeni n-p* prijelaz ima znatno manji intenzitet. 

Koristeći četverodimenzijske plohe potencijalne energije u normalnim koordinatama istraživana je dinamika intramolekularne vodikove veze u malonaldehidu i acetilacetonu. Izračunati vibracijski spektri ukazuju na snažno sprezanje niskofrekventnih modova koji uključuju istezanje vodikove veze i visokofrekventnog istezanja OH (OD) veze. Radili smo i na analitičkom oblikovanju multirezonantnih laserskih pulseva namijenjenih kontroli prijenosa populacije u općenitim kvantnim sustavima.

Research programme and results:

A theoretical investigation into unimolecular decomposition paths of primary (POZF) and secondary (SOU) fluorozonide was carried out by utilizing the multiconfigurational CASSCF/cc-pVTZ level in optimizations of the stationary points and calculations of the harmonic vibrational frequencies. The dynamical electron correlation was accounted for via the multireference CASPT2/cc-pVTZ treatment based on the zeroth-order CASSCF/cc-pVTZ reference. The CASPT2 was substituted with the CCSD(T)/6-31IG(2d,2p) correction whenever the former resulted in negative activation barriers. The most favorable decomposition route of POZF is a concerted cleavage to carbonyl oxide (CO) and formyl fluoride (FF) with fragments in the anti conformation, with regard to the orientation of the terminal oxygen in the carbonyl oxide and the flourine atom of the carbonyl compound. The ratio of unimolecular rate constants calculated within the RRKM formalism suggests that the CO-FF channel of cleavage amounts to 98%, which agrees well with the upper bound of experimental esimates. The SOZF decomposition most readily takes place in a stepwise manner initiated by the O-O bond rupture. Two conformational minima are exhibited by SOZF, the O-O and H2C-O half-chairs. The calculated rotational constants and scaled frequencies for the 0-0 half-chair are in good agreement with the experimental values.

The pi-pi* and n-pi* valence excited states of dibenzo-p-dioxin (DD) were studied via the complete active space SCF and multiconfigurational second-order perturbation theory employing the cc-pVDZ basis set and the full pi-electron active spaces of 16 electrons in 14 active orbitals. The geometry and harmonic vibrational wavenumbers of the ground state correlate well with the experimental and other theoretical data. In particular, significant improvements over previously reported theoretical results are observed for the excitation energies. All of the pi-pi* excited states exhibit planar D-2h minima. Thus no evidence was found for a C-2v butterfly-like relaxation, although the wavenumbers of the b(3u), butterfly flapping mode proved exceedingly low in both the ground S-0((1)A(g)) and the lowest dipole allowed excited S-1(B-1(2u)) state. The calculations of oscillator strengths established the 2(1)B(2u) <- 1(1)A(g) and 2(1)B(1u) - 1(1)A(g) transitions as by far the most intense, whereas the only allowed of the n-pi* transitions (B-1(3u)) should possess only a modest intensity. Studies into dependence of the oscillator strengths on the extent of the butterfly-like folding showed that the electronic spectrum is more consistent with a folded equilibrium geometry assumed by DD in solution.

The intramolecular hydrogen bond in the enol-acethylacetone (ACAC) is investigated by performing reduced-dimensional quantum calculations. To analyze the shared proton vibrations, two sets of coordinates were employed: normal mode coordinates describing the motion in the vicinity of the most stable configuration, and internal coordinates accounting for the double minimum proton motion. It is proved that the extreme broadness of the OH-stretch band in ACAC is a consequence of the coexistence of two enol-ACAC structures: the global minimum and the transition state for rotation of the distal methyl group. Further, a ground-state tunneling splitting of 116 cm(-1) is found, and it is shown that the inclusion of the kinematic coupling is mandatory when treating large-amplitude proton motion. In the OH-stretch direction a splitting of 853 cm(-1) was predicted.