Huasheng Wang

(2+1) REMPI spectra of Ω=0 states of the hydrogen halides: Spectroscopy, perturbations and excitation mechanisms

(2+1) REMPI spectra of HX (X=Cl, Br and I) have been recorded and analyzed by simulation calculations to derive rotational constants, band origins and isotope shift values for a number of vibrational bands of Ω=0 states. Our data for HCl compare nicely with those derived by Green et al. by conventional analysis methods [D. S. Green et al., J. Mol. Spectrosc. 150, 303, 354, 388 (1991); D. S. Green and S. C. Wallace, J. Chem. Phys. 96, 5857 (1992)]. New spectroscopic parameters were derived for eight vibrational bands which are assigned to the V(1Σ+) state, for v′=4 of the E(1Σ+) state, as well as for five new bands in HBr. New spectroscopic parameters were derived for four vibrational bands which are assigned to the V state and for v′=1 of the E state in HI. Anomalies observed in energy level spacings, rotational parameters and isotope shift values are interpreted as being largely due to homogeneous interactions between the V and the E states. It is argued that the interaction causes a compression of rovib...

Resonance enhanced multiphoton ionization of the hydrogen halides: Rotational structure and anomalies in Rydberg and ion-pair states of HCl and HBr

(2+1) resonance enhanced multiphoton ionization spectra have been recorded, simulated, and used to derive energies of rovibrational levels in the F(1Δ), E(1Σ+), and V(1Σ+) states for HCl (H35Cl and H37Cl) and HBr (H79Br and H81Br). Spectroscopic parameters derived for the F states compare nicely with those derived by others using conventional analysis methods. Clear evidence for near resonance interactions between the F and the V states is seen for the first time, both in HCl and HBr. Shape of curves for rotational level energy spacings versus rotational quantum numbers are found to depend characteristically on the nature of off-resonance interactions observed between the E and the V states. Model calculations for state interactions, based on perturbation theory, are performed for HCl. These prove to be useful to interpret observed perturbations, both qualitatively and quantitatively. Interaction strengths are evaluated for F to V and E to V state interactions. Variations observed in the intensity ratios ...

Three-photon absorption spectroscopy: the L(1Φ3) and m(3II1) states of HCl and DCl

Analysis of (3+1) REMPI room temperature spectra by use of three-photon absorption modelling allowed, for the first time, identification and characterization of Ω = 3, Φ states (L(1Φ3)) in HCl and DCl and of the m(3II1) state in DCl. Simulation analyses and determination of isotope shifts allowed evaluation of vibrational and rotational spectroscopic parameters for both states and both molecules. The mechanism of three-photon absorption in the m(3II1) ← X(1Σ+) transition is discussed.

What to see and what not to see in three-photon absorption: (3+1) REMPI of HBr

Honl–London type approximation expressions are derived for transition strengths of the Ω′=0,1,2,3, ←Ω″=0 (Σ, Π, Δ and Φ←Σ) three-photon transitions for diatomic molecules belonging to Hund’s case (a) and intermediate (a)–(b) coupling schemes. These are used to demonstrate what may be seen and what may not be seen in three-photon absorption spectra. The forms are used to simulate room temperature (3+1)REMPI spectra of HBr, for different electronic transitions. The analysis as well as comparison with (2+1)REMPI spectra is used to demonstrate the usefulness of three-photon absorption spectroscopy to identify excited states and to derive spectroscopic parameters. A Rydberg state, not observed in single or two-photon absorption, with band origin 82 837 cm−1 was identified and analyzed for the first time. It was assigned as the L1Φ(3) ((σ2π3)5dδ)) state, (0,0) band.

Photofragmentation, state interaction, and energetics of Rydberg and ion-pair states: Resonance enhanced multiphoton ionization of HI

Mass resolved resonance enhanced multiphoton ionization data for hydrogen iodide (HI), for two-photon resonance excitation to Rydberg and ion-pair states in the 69,600-72,400 cm(-1) region were recorded and analyzed. Spectral perturbations due to homogeneous and heterogeneous interactions between Rydberg and ion-pair states, showing as deformations in line-positions, line-intensities, and line-widths, were focused on. Parameters relevant to photodissociation processes, state interaction strengths and spectroscopic parameters for deperturbed states were derived. Overall interaction and dynamical schemes to describe the observations are proposed.

Two-Dimensional (2+n) REMPI of CH3Br: Photodissociation Channels via Rydberg States

(2+n) resonance enhanced multiphoton ionization (REMPI) spectra of CH(3)Br for the masses H(+), CH(m)(+), (i)Br(+), H(i)Br(+), and CH(m)(i)Br(+) (m = 0-3; i = 79, 81) have been recorded in the 66 000-81 000 cm(-1) resonance energy range. Signals due to resonance transitions from the zero vibrational energy level of the ground state CH(3)Br to a number of Rydberg states [Ω(c)]nl;ω (Ω(c) = 3/2, 1/2; ω = 0, 2; l = 1(p), 2(d)) and various vibrational states were identified. C((3)P) and C*((1)D) atom and HBr intermediate production, detected by (2+1) REMPI, most probably is due to photodissociation of CH(3)Br via two-photon excitations to Rydberg states followed by an unusual breaking of four bonds and formation of two bonds to give the fragments H(2) + C/C* + HBr prior to ionization. This observation is supported by REMPI observations as well as potential energy surface (PES) ab initio calculations. Bromine atom production by photodissociation channels via two-photon excitation to Rydberg states is identified by detecting bromine atom (2+1) REMPI.

REMPI spectra of I2. The [32]c5d; 1g Rydberg state and interactions with ion pair states

Abstract Rotational contours of the (2+1) REMPI spectra of iodine due to resonance excitation to the [ 3 2 ] c 5d; 1g Rydberg state have been recorded at room temperature. Rotational parameters, B itv , were estimated from the band-head structure and used to derive the band origin by spectral simulations. T e =59683.9±1.5 cm −1 and ω e =248.5±0.6 cm −1 were obtained from vibrational analyses. Several anomalies observed in the vibrational and band-head structures are discussed and interpreted as being due to the homogeneous interaction between the Rydberg state and the β(1g) ion pair state.

Rotational perturbations in the (2 + 1) REMPI spectrum of the Rydberg state [2Π32]c5d;1g of I2

Abstract Partly rotationally resolved (2 + 1) resonance-enhanced multiphoton ionization contour spectra of the vibrational bands corresponding to the [ 2 Π 3 2 g ] c 5 d; lg → → X transition in iodine, recorted at room temperature, have been analyzed. Irregular band spectral structures could be simulated by assuming rotational line strengths to be dependent on rotational quantum number in the resonantly excited state at the two-photon level. The analysis allowed improved rotational constants ( B v′ , and D v′ ) and corresponding internuclear distances ( r v ′ ) for the Rydberg state to be evaluated, as well as the characteristic rotational parameters, B′ e = 0.04047 ± 0.00010 cm −1 , α′ e = (1.3 ± 0.2)× 10 −4 cm −1 and r′ e = 2.562 ± 0.003 A. The anomalies in the rotational structure are ascribed to perturbation effects due to heterogeneous interaction between an ion-pair state and the Rydberg state. A candidate for the perturbing state is the D′(2g) state.

Resonance-Enhanced Multiphoton Ionization of CH2Br2: Rydberg States, Photofragmentation, and CH Spectra

Mass-resolved (2 + n) resonance-enhanced multiphoton ionization (REMPI) spectra of CH2Br2 in the two-photon resonance excitation region from 71 200 to 82 300 cm(-1) were recorded and analyzed. Spectral structures allowed characterization of new molecular Rydberg states. C*((1)D2) was found to be an important intermediate in the photodissociation processes. A broad spectral feature peaking at about 80 663 cm(-1) in the C(+) spectrum and frequently seen in related studies is reinterpreted and associated with switching between three- and two-photon ionization of C*((1)D2). Analysis of band structures due to transitions from the A(2)Δ state of CH* that were seen in the CH(+) and C(+) REMPI spectra allowed characterization of three electronic states of CH, assigned as E(2)Π, D(2)Π, and F(2)Σ(+), which clarifies a long-term puzzle concerning the energetics of the CH radical. Predissociation of the E, D, and F states to form C*((1)D2) occurs. Bromine atomic lines were observed and are believed to be associated with bromine atom formation via predissociation of CH2Br2 Rydberg states.