Photodissociation dynamics of dichlorocarbene at 248 nm

Abstract

The dynamics of the 248 nm photodissociation of the CCl(2) molecule have been investigated in a molecular beam experiment. The CCl(2) parent molecule was generated in a molecular beam by pyrolysis of CHCl(3), and both CCl(2) and the CCl photofragment were detected by laser fluorescence excitation. The 248 nm attenuation cross sections was estimated from the reduction of the CCl(2) signal as a function of the photolysis laser fluence. The internal state distribution of the CCl photofragment was derived from analysis of laser fluorescence excitation spectra in the A (2)Delta- X (2)Pi band system. The CCl(X (2)Pi, nu = 0) rotational state distribution was found to be bimodal, with maximum populations at N approximately 10 and 85, and was dependent upon the source backing pressure, and hence upon the internal state distribution of the CCl(2) precursor. The 248 nm photodissociation dynamics appears to involve two separate channels, namely nearly impulsive rotational energy release and predissociation with little rotational energy imparted to the CCl fragment.

Spectroscopy and dynamics of the predissociated, quasi-linear S2 state of chlorocarbene

“…Recently, Dagdigian and co-workers examined the photodissociation dynamics of a number of triatomic halocarbenes, including CHCl, at wavelengths of 248 and 193 nm. [11][12][13][14][15] In the case of CHCl, the diatomic product of the higher lying radical channel (forming CH( 2 ) + Cl) was detected via Laser Induced Fluorescence (LIF), following excitation of the parent carbene at 193 nm. 15 The CCl product of the lowest radical channel (forming CCl( 2 ) + H) could not be detected due to the large background of this radical in the beam.…”

Observation of the predissociated, quasilinear B̃(A′1) state of CHF by optical-optical double resonance

“…The ultraviolet ͑248 and 266 nm͒ photodissociation of CCl 2 has been explored recently, however, the identity of the dissociative surface remains uncertain. 8 Even for the simplest carbene, CH 2 , weak transitions in the c 1 A 1 ← ã 1 A 1 system observed some 60 years ago 9 remained unassigned until very recently when rotationally resolved spectra of the c state were observed using optical-optical double resonance ͑OODR͒ spectroscopy. [10][11][12] The energies accessed in the c state were just below the barrier to dissociation.…”

Spectroscopic Study of the Ã1A" - X~1A' System of CHBr

“…[17][18][19] The CHBr molecule was prepared in a supersonic beam by flash pyrolysis of a dilute mixture (5-10% mole fraction) of CH 3 Br in argon (total pressures of 1 atm) by passage through a resistively heated SiC tube (0.5 mm ID, 2 mm OD) attached to a pulsed solenoid valve (General Valve). The experimental chamber housing the molecular beam was evacuated with a 10 in.…”

“…Considerable information is now available on the electronic transition to the first excited electronic state ( 1 B 1 ) of a number of halocarbenes, and vibrational energies and rotational constants in both ground and excited electronic states have been determined. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] This has allowed determination of molecular geometries and information on the relevant potential energy surfaces. The 1 A 1 and 1 B 1 states coalesce to a degenerate electronic state at linear geometry, thus leading to the Renner-Teller effect which couples the two states.…”

“…[17][18][19] The internal state distributions of the CCl and CF fragments from the 193 and 248 nm photolysis of CCl 2 and CFCl, respectively, have been determined. In addition, it was also possible to determine attenuation cross sections of the parent molecules by monitoring their densities versus the fluence of the excimer laser.…”