We report the observation and assignment of the ν2 fundamental vibration in the HOCO and DOCO radicals. The radical was made by the photolysis of acetic acid or acetic acid-d at 193 nm in a flow system. The observed spectra indicate that the excited vibrational level is perturbed in both HOCO and DOCO. In HOCO, the rotational levels in ν2=1 have an irregular dependence on the Ka quantum number, probably caused by anharmonic interactions with combinations of lower frequency in plane vibrations. An a-type Coriolis interaction involving perturbation by a level containing one quantum of the out-of-plane torsional vibration cannot be rigorously excluded however. In DOCO, there are also N-dependent perturbations in the excited state. Only parallel transitions were assigned in the ν2 fundamental of both isotopomers. The K=0 band origin for HOCO is at 1852.567 cm−1 which compares with 1843.7 cm−1 reported previously for the radical trapped in a low-temperature argon matrix. This absorption spectrum will be useful in future studies of chemical reactions involving the radical.

A number of vibrational bands of the à 2Σ+↔X̃ 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 à state with clear evidence for at least some electronic reorganization between Ar and the open-shell OH radical in the complex. Conversely, the X̃ state appears to be bound almost solely by physical van der Waals interactions characteristic of systems containing only closed-shell species.

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.

Articles you may be interested inHigh resolution electronic spectroscopy of ArOH and ArOD vibronic bands J. Chem. Phys. 97, 7999 (1992); 10.1063/1.463423 Rotational, fine, and hyperfine structure in the highresolution electronic spectrum of ArOH and ArOD J. Chem. Phys. 95, 7086 (1991); 10.1063/1.461437Observation of the pure rotational spectra of the ArOH and ArOD complexes by a Fouriertransform microwave spectrometer J. Chem. Phys. 95, 7001 (1991);Laser induced fluorescence spectra of the ArOH bands associated with electronic excitation of the OH A-X(v' = 0 -v" = 0) transition were reported previously. An extensive search in the vicinity of the OH/ODA e:1:to the observation of 36 vibronic bands which were identified as belonging to ArOH or ArOD complexes. All of the bands were found to originate from the 20(3/2)' v" = 0 ground electronic state of the OH/OD radical. Two distinguishable vibronic structures were identified. A lower energy vibrational progression was assigned to the van der Waals stretch. This band system was designated as the "A .. bands. A higher energy set of bands exhibited a different vibrational structure which did not fit a simple vibrational mode progression. These bands were labeled as the" U" system. Spectra showing partially resolved rotational structure were recorded for all of the observed ArOH/ ArOD bands. The A and U systems were also distinguished by differences in their rotational structure and effects of HID substitution on the vibrational and rotational parameters. Preliminary rotational analysis gave ground state constants (B;;) of 0.100 cm -I for ArOH and 0.098 em -I for ArOD. (B; constants for the excited state of the A system were determined to be 0.178 cm -I for ArOH and 0.168 cm -I for ArOD. These rotational constants show that the Ar-OH/ Ar-OD van der Waals bond has been considerably shortened upon electronic excitation. This suggests that partial charge transfer might contribute to the stability of ArOH and ArOD complexes in the excited electronic state. Observed spectra and results of rovibronic analysis are discussed.