Multiphoton ionization processes in HCl studied by photoelectron spectroscopy

Molecular beam cooled HCl was state selected by two-photon excitation of the V (1) summation operator(0(+)) [v=9,11-13,15], E (1) summation operator(0(+)) [v=0], and g (3) summation operator(-)(0(+)) [v=0] states through either the Q(0) or Q(1) lines of the respective (1,3) summation operator(0(+))<--<--X (1) summation operator(0(+)) transition. Similarly, HBr was excited to the V (1) summation operator(0(+)) [v=m+3, m+5-m+8], E (1) summation operator(0(+)) [v=0], and H (1) summation operator(0(+)) [v=0] states through the Q(0) or Q(1) lines. Following absorption of a third photon, protons were formed by three different mechanisms and detected using velocity map imaging. (1) H(*)(n=2) was formed in coincidence with (2)P(i) halogen atoms and subsequently ionized. For HCl, photodissociation into H(*)(n=2)+Cl((2)P(12)) was dominant over the formation of Cl((2)P(32)) and was attributed to parallel excitation of the repulsive [(2) (2)Pi4llambda] superexcited (Omega=0) states. For HBr, the Br((2)P(32))Br((2)P(12)) ratio decreases with increasing excitation energy. This indicates that both the [(3) (2)Pi(12)5llambda] and the [B (2) summation operator5llambda] superexcited (Omega=0) states contribute to the formation of H(*)(n=2). (2) For selected intermediate states HCl was found to dissociate into the H(+)+Cl(-) ion pair with over 20% relative yield. A mechanism is proposed by which a bound [A (2) summation operatornlsigma] (1) summation operator(0(+)) superexcited state acts as a gateway state to dissociation into the ion pair. (3) For all intermediate states, protons were formed by dissociation of HX(+)[v(+)] following a parallel, DeltaOmega=0, excitation. The quantum yield for the dissociation process was obtained using previously reported photoionization efficiency data and was found to peak at v(+)=6-7 for HCl and v(+)=12 for HBr. This is consistent with excitation of the repulsive A(2) summation operator(12) and (2) (2)Pi states of HCl(+), and the (3) (2)Pi state of HBr(+). Rotational alignment of the Omega=0(+) intermediate states is evident from the angular distribution of the excited H(*)(n=2) photofragments. This effect has been observed previously and was used here to verify the reliability of the measured spatial anisotropy parameters.

Section: Introductionmentioning

confidence: 99%

Proton formation in 2+1 resonance enhanced multiphoton excitation of HCl and HBr via (Ω=) Rydberg and ion-pair states

Romanescu

Loock

2007

“…1, which is a composite of available data, calculations, and comparison to HCl. 8,16,17 In this paper, we present a study of the dynamics of Rydberg E( 1 ⌺ ϩ ) state/ion-pair state V( 1 ⌺ ϩ ) using a femtosecond laser pump-probe technique coupled with reflectron time-of-flight mass spectrometry. The lifetime of HBr in this state is determined over a range of pump laser wavelengths and the influence of deuterium isotope substitution is also investigated.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the E state of HBr and DBr: Evidence for the role of tunneling

Hurley

Zhong

Castleman

2000

Extensive ab initio study of the valence and low-lying Rydberg states of BBr including spin-orbit coupling A unified model of the dynamics and spectroscopy of the g 3 Σ 0 − and E 1 Σ + states of hydrogen chloride J. Chem. Phys. 108, 984 (1998); 10.1063/1.475461 Time and frequency resolved spectra of high molecular Rydberg states by dynamical computationsThe dynamics of the interaction of the Rydberg E( 1 ⌺ ϩ ) state and the valence state V( 1 ⌺ ϩ ) of HBr and DBr were investigated using a reflectron time-of-flight mass spectrometer coupled with a femtosecond laser system. Interrogation of the state formed by the avoided crossing of the Rydberg and valence states revealed dynamic behavior that was different for the two isotopes. Pump-probe experiments on HBr showed no change in the lifetime over the range of pump wavelengths of 256.7-254.7 nm. However, the lifetime of DBr decreased as the pump wavelength was tuned bluer. Tunneling is involved in the evolution of the population in photoexcited Rydberg state to the ion-pair state.

“…5,[12][13][14][15] Spectra and images of those states were therefore only used to aid laser wavelength calibration and to assign the fragmentation channels in the images. The spectroscopy and ionization dynamics of the g and F state confirmed previous reports and contained no surprises.…”

Section: Resultsmentioning

confidence: 99%

“…In a photoelectron spectroscopic experiment, de Lange and co-workers have shown that the main source of photoelectrons arising from excita-tion of the ϭ9 level of the V 1 ⌺ ϩ (0 ϩ ) state is the photoionization of the excited hydrogen and chlorine atoms formed following dissociation of a superexcited state. 5 Based on earlier work by Lefebvre-Brion and Keller, 6 it was suggested that this state is a 1 ⌺ ϩ (0 ϩ ) state derived from a (5 1 2 4 )4s configuration, i.e., the lowest member of a Rydberg series converging to the first excited state of the HCl ϩ ion. 2 There exists therefore plenty of evidence that the direct ionization of those Rydberg states which may mix with the ion pair state will have to compete with photodissociation into excited state atoms, through a superexcited ''gateway'' state.…”

Section: Introductionmentioning

confidence: 99%

Superexcited state reconstruction of HCl using photoelectron and photoion imaging

Romanescu

Manzhos

Boldovsky

et al. 2004

The velocity-map imaging technique was used to record photoelectron and photofragment ion images of HCl following two-photon excitation of the E Sigma(+)(0+), V 1Sigma(+)(0+) (nu=9,10,11) states and subsequent ionization. The images allowed us to determine the branching ratios between autoionization and dissociation channels for the different intermediate states. These branching ratios can be explained on the basis of intermediate state electron configurations, since the configuration largely prohibits direct ionization in a one-electron process, and competition between autoionization and dissociation into H* (n=2)+Cl and H+Cl*(4s,4p,3d) is observed. From a fit to the vibrationally resolved photoelectron spectrum of HCl+ it is apparent that a single superexcited state acts as a gateway to autoionization and dissociation into H+Cl*(4s). Potential reconstruction of the superexcited state to autoionization was undertaken and from a comparison of different autoionization models it appears most likely that the gateway state is a purely repulsive and low-n Rydberg state with a (4Pi) ion core.