Galina Kerenskaya

Spectroscopy and dynamics of I2(B)–Ne

The I2–Ne complex has been examined using double resonance and fluorescence depletion techniques. Action spectra for I2(B,v)–Ne, detected by monitoring the I2(B,v−1) predissociation fragments, show that the Δν=−1 predissociation channel is less efficient for levels above v=32 (with no excitation of the intermolecular vibrations), and closed for v>36. From these data we obtained a revised estimate for the dissociation energy for I2(B)–Ne of D0=57.6±1.0 cm−1. Action spectra for I2(B,v=34)–Ne, detected by monitoring I2(B,v=33) fragments, revealed a progression of intermolecular vibrational levels that had not been observed previously. These levels have been assigned to T-shaped, linear, and delocalized states of I2(B,v=34)–Ne. Assignments were based on characteristic vibrational distributions exhibited by the I2(B,v−Δv) predissociation fragments. Fluorescence depletion measurements show that all of the bands in the action spectrum originate from a common ground state level. Furthermore, the one atom cage eff...

Experimental detection and theoretical characterization of the H2–NH(X) van der Waals complex

The H2-NH(X) van der Waals complex has been examined using ab initio theory and detected via fluorescence excitation spectroscopy of the A(3)Pi-X(3)Sigma(-) transition. Electronic structure calculations show that the minimum energy geometry corresponds to collinear H2-NH(X), with a well depth of D(e)=116 cm(-1). The potential-energy surface supports a secondary minimum for a T-shaped geometry, where the H atom of NH points towards the middle of the H2 bond (C(2v) point group). For this geometry the well depth is 73 cm(-1). The laser excitation spectra for the complex show transitions to the H2+NH(A) dissociative continuum. The onset of the continuum establishes a binding energy of D(0)=32+/-2 cm(-1) for H2-NH(X). The fluorescence from bound levels of H2-NH(A) was not detected, most probably due to the rapid reactive decay [H2-NH(A)-->H+NH2]. The complex appears to be a promising candidate for studies of the photoinitiated H2+NH abstraction reaction under conditions were the reactants are prealigned by the van der Waals forces.

Experimental and theoretical investigation of the c 1Π–a 1Δ transition of NH/D–Ne

A study of NH/D–Ne was undertaken to investigate the structure of this complex and examine the ability of high-level theoretical methods to predict its properties. The c 1Π–a 1Δ transition was characterized using laser induced fluorescence measurements. Spectra recorded in the vicinity of the monomer show groups of complex features associated with the monomer P(2), Q(2), and R(2) lines. The present study focused on the low-energy bands associated with P(2). Results from theoretical calculations were used to guide the interpretation of the spectra. Two-dimensional potential energy surfaces were calculated using second-order multireference perturbation theory with large correlation consistent basis sets. The potential surfaces were used to predict the rovibronic structure of the c–a system. Calculated rovibronic energy level patterns could be recognized in the spectra but quantitative discrepancies were found. For the a and c states the ab initio potentials were found to be too shallow, and for the c state ...

Potential energy surfaces for CH(A 2Δ)–Ar and analysis of the A 2Δ–X 2Π band system

Two-dimensional intermolecular potential energy surfaces for the CH(A 2Δ)–Ar complex (CH bond fixed at equilibrium) have been calculated at the multireference singles and doubles configuration interaction/correlation-consistent valence quadruple zeta level of theory. These surfaces are of 2 2A′ and 2 2A″ electronic symmetry. Both potentials define a linear CH–Ar equilibrium structure (Ar…H∼3 A), with a secondary minimum for the Ar–CH linear geometry (Ar…C∼4 A). The global minimum is ∼117 cm−1 below dissociation. Side-on approach of the Ar atom breaks the orbital degeneracy of the 2Δ state, but this splitting is relatively small near the equilibrium separation, only about 10 cm−1. The potential surfaces have been used in simulations of the A–X bands of CH/D–Ar. The correlation between the simulated and observed spectra was sufficient for assignment of the latter. Systematic adjustment of the A state average potential, defined as Va=(VA′+VA″)/2, was made to obtain a surface that reproduces the vibrational e...

Spectroscopic and theoretical characterization of the AΔ2-XΠ2 transition of CH–Ne

The AΔ2-XΠ2 transition of CH–Ne was examined using laser-induced fluorescence and fluorescence depletion techniques. The spectrum was found to be particularly congested due to the large number of bound states derived from the CH(A,n=2)+Ne interaction, and the small energy spacings between these states resulting from the relatively weak anisotropy of the van der Waals bond. High-level ab initio calculations were used to generate two-dimensional potential energy surfaces for CH(X)−Ne and CH(A)−Ne. The equilibrium structures from these surfaces were bent and linear for the X and A states, respectively. Variational calculations were used to predict the bound states supported by the ab initio surfaces. Empirical modification of the potential energy surfaces for the A state was used to obtain energy-level predictions that were in good agreement with the experimental results. Transitions to all of the optically accessible internal rotor states of CH(A,n=2)−Ne were identified, indicating that CH performs hindered...

Experimental and theoretical investigation of the A 3Pi - X 3Sigma- transition of NH/D-Ne

A study of NH/D-Ne was undertaken to investigate the structure of this complex and examine the ability of high-level theoretical methods to predict its properties. The A 3pi-X 3sigma- transition was characterized using laser induced fluorescence measurements. Results from theoretical calculations were used to guide the interpretation of the spectra. Two-dimensional potential energy surfaces were calculated using second-order multireference perturbation theory with large correlation consistent basis sets. The potential energy surfaces were used to predict the ro-vibronic structure of the A-X system. Calculated ro-vibronic energy level patterns could be recognized in the spectra but quantitative discrepancies were found. These discrepancies are attributed to incomplete recovery of the dynamical correlation energy.