Infrared spectroscopy and anharmonic theory of H3 +Ar2,3 complexes: The role of symmetry in solvation.

The vibrational spectra of H3 +Ar2,3 and D3 +Ar2,3 are investigated in the 2000 cm-1 to 4500 cm-1 region through a combination of mass-selected infrared laser photodissociation spectroscopy and computational work including the effects of anharmonicity. In the reduced symmetry of the di-argon complex, vibrational activity is detected in the regions of both the symmetric and antisymmetric hydrogen stretching modes of H3 +. The tri-argon complex restores the D3h symmetry of the H3 + ion, with a concomitant reduction in the vibrational activity that is limited to the region of the antisymmetric stretch. Throughout these spectra, additional bands are detected beyond those predicted with harmonic vibrational theory. Anharmonic theory is able to reproduce some of the additional bands, with varying degrees of success.

Communication: Trapping a proton in argon: Spectroscopy and theory of the proton-bound argon dimer and its solvation.

Ion-molecule complexes of the form H+Arn are produced in pulsed-discharge supersonic expansions containing hydrogen and argon. These ions are analyzed and mass-selected in a reflectron spectrometer and studied with infrared laser photodissociation spectroscopy. Infrared spectra for the n = 3-7 complexes are characterized by a series of strong bands in the 900-2200 cm-1 region. Computational studies at the MP2/aug-cc-pVTZ level examine the structures, binding energies, and infrared spectra for these systems. The core ion responsible for the infrared bands is the proton-bound argon dimer, Ar-H+-Ar, which is progressively solvated by the excess argon. Anharmonic vibrational theory is able to reproduce the vibrational structure, identifying it as arising from the asymmetric proton stretch in combination with multiple quanta of the symmetric argon stretch. Successive addition of argon shifts the proton vibration to lower frequencies, as the charge is delocalized over more ligands. The Ar-H+-Ar core ion has a first solvation sphere of five argons.

A comparison of language deficits in learning-disabled, head-injured, and nondisabled young adults: results from an abbreviated Aphasia Screening Test.

This study used an Aphasia Screening Test (AST) abbreviated to its naming, pronunciation, and sentence interpretation items to compare groups of 60 learning-disabled (LD), 30 head-injured (HI), and 30 nondisabled (ND) young adults matched for FISQ and balanced for gender composition. The LD and HI, who did not differ, made significantly more AST errors than the ND. One-quarter to one-third of the LD and HI subjects exhibited language deficits. For the clinical groups only, AST errors, particularly pronunciation errors, were related negatively to WRAT reading and spelling scores. The Reitan and Wolfson (1988) severity ratings for AST items did not improve group discrimination.

Encoding and retrieval processes in learning-disabled, head-injured, and nondisabled young adults.

Using a multi-trial, free-recall paradigm (Rey Auditory-Verbal Learning Test; Lezak, 1983), the acquisition and retention by learning disabled (LD) young adults with a Halstead Impairment Index less than or equal to 0.3 (low LD) or greater than or equal to 0.4 (high LD) was compared with that of nondisabled and head-injured (HI) young adults. Significant group differences, particularly during the last three acquisition trials, confirmed the effectiveness of this method in revealing subtle learning and retention deficits. Analyses of Trial 1 recall showed group differences in the prerecency but not the recency portion of the serial position curve, thus implicating long-term but not short-term memory differences between the groups. Analyses of pair frequency (Sternberg & Tulving, 1977) data showed that the three clinical groups had difficulty organizing the to-be-learned material for effective retrieval. Following an interpolated task, retention was poorer for the clinical groups than for the nondisabled and varied inversely with the degree of neuropsychological impairment. Finally, during retention, the nondisabled and low LD groups retained and used the list organization established during acquisition whereas the high LD and HI groups did not.

Phonetically inaccurate spelling among learning-disabled, head-injured, and nondisabled young adults.

We applied the Boder and Jarrico (1982, The Boder Test of Reading-Spelling Patterns, New York: Grune & Stratton) criteria to the WRAT spelling list and examined the phonetically inaccurate spelling error patterns of learning-disabled (LD), head-injured (HI), and nondisabled young adults. Phonetically inaccurate (PI) errors were reliably rated (interrater r = .94) and were correlated significantly more strongly with dysphasic errors (r = .33) than with dyscopia (r = .16). ANOVA showed that LD and HI, which did not differ, made significantly more PI errors than both nondisabled and HI. These results indicate that PI errors reflect an underlying language disorder. The results also suggest that PI errors are more frequent in brain-related disorders. Finally, when group differences in cognitive ability are statistically controlled, PI errors are more common only among LD persons.

Electrophysiological correlates of handedness and speech perception contrasts.

Auditory evoked responses (AERs) were recorded from left- and right-handed subjects who listened to consonant sounds from different phonetic categories. AERs recorded at parietal scalp regions indicated both groups differentiated categorical differences between speech sounds. However, hand preferences did not affect hemisphere responses to speech sounds.