Polanyi rules for ultrafast unimolecular reactions: simulations for HCo(CO)4(1E)* .fwdarw. hydrogen atom + cobalt tetracarbonyl

Abstract

The traditional Polanyi rules for control of bimolecular reactions by selective investment of energy, e.g. preferentially translational, not vibrational energy for early-downhill reactions on attractive potential energy surfaces, are extended to ultrafast unimolecular reactions. Specifically, we consider photodissociations of the metal-hydrogen bond of HCo(C0)4( lE), occurring on a time scale of approximately 20 fs, much faster than competing intramolecular vibrational energy redistribution (IVR). Here the reaction path toward the products H + C O ( C O )~ is hindered by a barrier located in the H + Co(CO)4 exit valley of the potential energy surface.In order to overcome this barrier and, therefore, to increase reactivity, vibrational energy should be invested selectively into the bond to be broken, i.e. [H-Co], not into complementary "spectator" modes, e.g. [CO-Co].The required energetic preparation of reactants may be achieved by selective IR + UV two-photon excitations or by alternative techniques including frequency-selective UV single-photon photodissociation. The Polanyi rules for unimolecular reactions are demonstrated by fast Fourier transform (FFT) propagations of representative wave packets.

Vibrationally enhanced associative photodesorption of molecular hydrogen from Ru(0001)

“…7b, its Husimi transform below. One notes that the pulse is ''late'', to avoid dissipation, with a center frequency around x % x (00), (20) . Note also that the excitation is not as mode-selective as for the Z-mode, since states with excitations in Z are also populated.…”

“…In particular, the IR + UV/vis strategy investigated here has its roots in many earlier contributions, notably of the Manz group (see Refs. [9,20]). …”

“…Our strategy is similar to ''vibrationally mediated chemistry'' in gas phase dynamics [17][18][19][20], where mode-and isotope-selective IR excitation using shaped laser pulses has been realized for systems with only a few modes [18]. It appears much more difficult to achieve the same goal for complex systems, including condensed phases and adsorbates.…”

Photoactivity and UV Absorption Spectroscopy of RCo(CO)4 (R = H, CH3) Organometallic Complexes

“…In most cases this primary reaction competes with the homolysis of a metal-metal bond (Mn 2 -(CO) 10 ), 1 metal-alkyl bond (RMn(CO) 3 (R-diimine), R ) methyl, ethyl, benzyl), 2 metal-methyl bond (MeMn(CO) 5 , 3 MeCo(CO) 4 ), 4 or metal-hydrogen bond (HCo(CO) 4 , HMn-(CO) 5 ). 5,6 Despite the number of experimental and theoretical studies devoted to this class of compounds, the knowledge of their electronic spectroscopy and photoreactivity is still limited.…”

Nonadiabatic Effects in the Photodissociation and Electronic Spectroscopy of HMn(CO)3(dab): Quantum Wave Packet Dynamics Based onab InitioPotentials

“…[15][16][17][18] In a second step, time-dependent quantum wave packet propagation methods can be used to characterize the photodissociation dynamics. [19][20][21][22] Additionally, the time-dependent wave packet approach may also be employed to calculate electronic emission or absorption spectra. 23,24 For the model diimine complex HMn(CO) 3 (dab) (dab ) 1,4-diaza-1,3-butadiene), we have speculated in a recent work 25 on the basis of the potential energy curves (PECs) computed for the metal-hydrogen bond cleavage reaction that an unbound 3 LLCT (ligand-to-ligand charge transfer) (σ f π*) excited state might be responsible for the metal-hydrogen bond homolysis.…”