Isotope effects in the dissociation of the B̃A11 state of SiH2, SiHD, and SiD2 using three-dimensional wave packet propagation

Abstract

Dissociations after the A 1B1-->B 1A1 photoexcitation of SiH2, SiHD, and SiD2 were studied to investigate excited-state dynamics and effects of the initial vibrational state. The cross section (sigma) for the photodissociation relative to SiH2(B)-->Si(1D)+H2 and the rovibrational population of the H2 fragment were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces (PESs) of the A and B electronic states and the transition dipole surfaces, which were reported in our previous paper [J. Chem. Phys. 122, 144307 (2005)]. The photodissociation spectrum consists of a broadband and a number of sharp peaks. For SiH2 and SiD2, the sharp peaks correspond to the resonance structure of the vibrational levels of the B state and the broadbands are nearly independent of the photon energy. The broadband for SiHD increases steeply with the photon energy above 30,000 cm(-1). The flux leaving the computational grid for SiH2 and SiD2 consists of at least two components, whereas that for SiHD consists of only a faster component. These large isotope effects were discussed based on the valley to the dissociation channel on PES and the difference in the position of the initial wave packet for three isotopomers.

Accurate ab initio based global adiabatic potential energy surfaces for the 13A′′, 13A′ and 21A′ states of SiH2

“…After that, Tokue et al 27 developed ab initio interpolated PESs for the X 1 A 1 , A 1 B 1 and B 1 A 1 states and then studied the photolysis process. 28 The conical intersection in the reaction system was systematically studied by means of high level ab initio calculations, 29 and the geometric phase effect related to conical intersections (CIs) was proved by Wu et al 30 Recently, Clark et al 31 conducted a comprehensive theoretical study of the rotation-vibration spectrum of ground state electrons using the newly constructed PES and the associated dipole moment which achieved good agreement with the experiment. Most recently, Cao and colleagues 32 investigated the deuterated isotope change quantum dynamics and cyclic polymer molecular dynamics of Si ( 1 D) + H 2 (X 1 S + g ) -H ( 2 S) + SiH (X 2 P) reactions on the global PES of SiH 2 constructed by the permutation invariant polynomial neural network (PIP-NN) method, while a three-dimensional (3D) PES using many-body expansion (MBE) theory 33,34 to study the integral cross-section (ICS) for the Si ( 1 D) + H 2 (X 1 S + g ) -H ( 2 S) + SiH (X 2 P) reaction was investigated in our preceding paper.…”

Ab initio conical intersections for the Si(1D) + H2 reaction system: a lowest five singlet states study

“…23 Before long, Tokue et al evaluated the transition probabilities of theX 1 A 1 -Ã 1 B 1 and A 1 B 1 -B 1 A 1 systems of SiH 2 and SiD 2 , 24 and they also investigated the photodissociation process of SiH 2 (Ã 1 B 1 ) / SiH 2 (B 1 A 1 ) / Si( 1 D) + H 2 . 25 Conical intersections (CIs), 26 not isolated geometries but form a seam, 27 are widespread in polyatomic systems and play a key role in non-adiabatic processes, 28,29 such as chargetransfer reaction, 30,31 nonradiative transition, and electronic quenching. At a CI, the Born-Oppenheimer approximation stipulating that electronic and nuclear motions are separable breaks down.…”

Detection and characterization of singly deuterated silylene, SiHD, via optical spectroscopy

“…RennerTeller effects were ignored. In a subsequent paper, 46 the same group investigated excited-state dynamics and the vibrational state dependence of the dissociations following theà 1 B 1 →B 1 A 1 photoexcitation using three dimensional wave packet propagation methods. As part of that study, the vibronic energies for theX 1 A ′ ,à 1 A ′′ , andB 1 A ′ states of SiHD were also calculated.…”

“…Modelling the role of SiH 2 in the fabrication of amorphous silicon thin films and polycrystalline silicon has also attracted significant interest. [1][2][3][4][5][6] Motivated primarily by the desire to garner a fundamental understanding of the properties of this simplest of silicon containing polyatomic molecules, and in part by the desire to develop a real time, in situ SiH 2 monitoring scheme, there have been numerous reported experimental and theoretical [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] studies of gas-phase SiH 2 , and to a lesser extent SiD 2 . In addition, SiH 2 is predicted to be abundant in circumstellar envelopes of carbon rich stars 49 and has been tentatively identified 50,51 via the detection of the 1 11 -0 00 pure rotational transition.…”

“…28 The spectra were interpreted as quasilinear behavior in theB 1 A 1 state with a very small barrier ( 125 cm −1 ) to linearity. Now turning to the theoretical studies, there have been numerous ab initio predictions of the properties of SiH 2 , with particular emphasis on understanding the state ordering [29][30][31][32][33][34][35][39][40][41][42]47 relative to that of CH 2 , to gain insight into the unimolecular dynamics, 36,46,48 and aid in the interpretation of the spectra. 37,[43][44][45][46] In addition to these electronic structure prediction, Duxbury et al 38 reanalyzed the originally recorded X 1 A 1 →à 1 B 1 absorption spectra of SiH 2 7,8 and rationalized the strong local perturbations and observed anomalous radiative lifetimes 14 43 In that study, ab initio calculations of the potential energy surfaces (PESs), the electric dipole moments, and the electric dipole transition moment surfaces for theX 1 A 1 andà 1 B 1 were performed.…”