Xiaonan Zheng

Rotational, fine, and hyperfine structure in the high‐resolution electronic spectrum of ArOH and ArOD

A number of vibrational bands of the A 2Σ+↔X 2Π electronic spectrum of both ArOH and ArOD have been investigated by laser induced fluorescence with a high‐resolution, pulsed laser system yielding linewidths ≲250 MHz in the UV. This spectrum not only displays completely resolved rotational structure, but also fine and hyperfine structure. The hyperfine constants and precise interatomic distances derived from the rotational constants provide a very interesting picture of the electronic and geometric structure of the complex. The bonding is incipiently chemical in the A state with clear evidence for at least some electronic reorganization between Ar and the open‐shell OH radical in the complex. Conversely, the X state appears to be bound almost solely by physical van der Waals interactions characteristic of systems containing only closed‐shell species.

Spectroscopy of metastable species in a free‐jet expansion: The D’←A’ transition of I2

The A’2u 3Π state of I2 is observed in a free‐jet expansion of I2 in Ar, where it is prepared by ArF laser irradiation. Laser excitation spectra are recorded for 37 bands in the υ’←0‘ progression of the D’2g(3P2)←A’ transition. The spectra display rotational temperatures of ∼5 K. At the 0.08 cm−1 resolution of the probe laser, rotational congestion near the band origins necessitates analysis by a nonlinear least‐squares contour simulation method. Subsequent correlated fits of the band‐by‐band results are combined with other results to produce global constants valid for υ’=0–86, υ‘=0–32.

Spectroscopy and relaxation dynamics of I2Arn clusters. Geminate recombination and cluster fragmentation

I2Arn clusters yield visible and near‐UV emissions when excited to the states which correlate with the first ion‐pair manifold of I2. These states may be accessed by 193 nm excitation of ground‐state clusters, or near‐UV excitation of electronically metastable I2(A’ or A)Arm. Comparisons of the cluster and I2/Ar matrix spectra suggest that such excitations result in fragmentation and ‘‘melting’’ of the clusters prior to emission. 532 nm photodissociation of I2 within the clusters is followed by geminate recombination which populates the A’, A, and X states. The probability for ejection of the recombined I2 from the clusters during the relaxation process appears to be size dependent. These results represent tentative steps towards the study of I(2P3/2)+I(2P3/2) recombination in Ar clusters. They also indicate that dissociation, recombination, and fragmentation processes may be used as a general method for generating metastable species in supersonic expansions.

Electronic spectroscopy and vibrational predissociation dynamics of OH–Kr and OD–Kr

OH/D–Kr complexes have been characterized via laser excitation of the A–X system. Progressions of the OH/D–Kr stretch were seen in conjunction with the OH/D 0–0 and 1–0 transitions. Rotational analyses of 17 bands provided ground state rotational constants of B‘=0.0835 (OH–Kr) and 0.0806 cm−1 (OD–Kr). These constants correspond to an intermolecular separation of 3.78±0.01 A. Assignment of the A state vibrational levels was accomplished by means of the 84Kr/86Kr isotope effect. A lower limit for the dissociation energy of OH(A,v=0)–Kr of De ≳ 1840 cm−1 was derived from the vibrational constants. Extrapolation of the rotational constants yielded an equilibrium intermolecular separation of 2.67±0.12 A. The properties defined by the spectroscopic analysis indicated weak, van der Waals bonding in the ground state, and incipient chemical bonding in the excited state. Vibrational predissociation of OH/D–Kr was observed through homogeneous broadening of the rotational lines. The predissociation rates ranged from ...

Electronic spectroscopy and relaxation dynamics of OH–Ne and OD–Ne

The structure and dynamics of OH/D–Ne complexes have been probed via studies of the A–X electronic transition. Bands associated with the OH/D 0–0, 1–0, and 2–1 transitions have been rotationally resolved and analyzed. Closely similar progressions of van der Waals vibrational levels were seen in conjunction with each parent transition. In the A state, the observed levels were assigned to the zero point, the–Ne stretch fundamental, and internal rotor‐stretch combinations. From this data, the barrier to internal rotation was estimated to be 43 cm−1 and a lower limit of D’0>68 cm−1 was established for the OH/D(A)–Ne bond. Predissociation of OH/D(A,v=1,2)–Ne has been characterized by time‐ and wavelength‐resolved fluorescence measurements. Vibrational predissociation rates were found to be in the range of (2–6)×105 s−1. Fragment OH/D(A,v=0) rotational distributions indicated that vibration–rotation transfer was the primary decay channel. Electronic predissociation of OH(A,v=2)–Ne was observed. The rate for thi...

Observation and analysis of the β ← A transition of I2 in a free-jet expansion

Abstract The A 1 u 3 Π state of I 2 is detected in a free-jet expansion of I 2 in Ar, where it is prepared by ArF laser irradiation. Laser excitation spectra are recorded for ∼30 bands in the v ′ ← 0″ progression of the β1 g ( 3 P 2 ) ← A transition, spanning v ′ = 25–68. For the heavy I 2 molecule, the cold (5 K) rotational distributions in the initial level have peak population at J ≈ 7. This translates into spectra which, at the resolution of the probe laser (0.08 cm −1 ), are very congested near the band origins. These spectra are analyzed by a nonlinear least-squares contour simulation method. Subsequent correlated fits of the band-by-band results produce global constants which corroborate and extend the existing results for the rotational and vibrational constants of the β state.

Observation and analysis of the D'←A' transition of I2 in a free-jet expansion

Abstract The A′ state of I 2 is observed for the first time in a free-jet expansion, where it is prepared by ArF laser photolysis of I 2 /Ar mixtures in the expansion region. Six bands in the υv″ = 0 progression of the D′ ← A′ transition are studied by laser excitation spectroscopy, leading to the following improved spectroscopic constants (cm −1 ) for the A′ and D′ states: B ″ o = 0.028054, B ′ e = 0.020526, α′ e = 5.30 × 10 −5 , ω′ e = 103.953, ω e χ′ e = 0.2097, ω e γ′ e = 2.687 × 10 −4 .

Spectroscopy of charge-transfer transitions in jet-cooled IBr

Abstract The A′(2) and A(1) states of IBr were detected in a free-jet expansion of IBr in Ar, where they were prepared by ArF laser irradiation. The υ″ = 0–5 progressions of the D′(2) ← A′ transition, and the v ″ = 0 and 1 progressions of the β(1) ← A(1) transition were observed and recorded for both 127 I 79 Br and 127 I 81 Br. Rotationally resolved excitation spectra were recorded for 31 bands of the D′ ← A′(2), υ′ ← υ″ = 1 progression, and band heads were measured at low resolution for an additional > 220 bands of this system and > 100 bands of the β ← A transition. Analyses of these spectra yield improved spectroscopic parameters for previously unobserved regions of all four electronic states, including the first characterization of the lowest v levels in the A′ and A states.