Observation of a new phosphorus-containing reactive intermediate: electronic spectroscopy and excited-state dynamics of the HPBr free radical.
The A (2)A(')-X (2)A(") electronic spectra of jet-cooled HPBr and DPBr have been obtained for the first time using the pulsed electric discharge technique with a precursor mixture of PBr(3) and H(2)/D(2). Laser-induced fluorescence and single vibronic level emission spectra gave the bending and P-Br stretching frequencies in the ground and excited states of both isotopomers. Rotational analyses of the HPBr and DPBr 0(0) (0) bands showed small spin splittings characteristic of a doublet-doublet transition of an asymmetric-top molecule. From the ground- and excited-state rotational constants, effective (r(0)) structures were derived with r(")(PH)=1.4307(86) A, r(")(PBr)=2.2021(9) A, and theta(")=95.2(8) degrees, and r(')(PH)=1.434(31) A, r(')(PBr)=2.1669(26) A, and theta(')=115.5(16) degrees . In a few favorable cases, further hyperfine splitting of the spin-rotation energy levels has been observed, due to the excited-state Fermi contact interaction of the unpaired electron with the spin magnetic moment of the (31)P nucleus, with a(F) (')=0.064(9) cm(-1) for HPBr. Fluorescence depletion spectroscopy and lifetime measurements indicate that higher vibrational levels of the A (2)A(') state are predissociated by a X (2)A(") dissociative continuum. CCSD(T)/aug-cc-pVTZ calculations predict that the most likely dissociation process is HPBr (X (2)A("))-->PH((3)Sigma(-))+Br((2)P(u)).
Tackett
Brandon S
BS
Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
Clouthier
Dennis J
DJ